Method for using a passive element memory array incorporating reversible polarity word line and bit line decoders

ABSTRACT

Circuits and methods are described for decoding exemplary memory arrays of programmable and, in some embodiments, re-writable passive element memory cells, which are particularly useful for extremely dense three-dimensional memory arrays having more than one memory plane. In addition, circuits and methods are described for selecting one or more array blocks of such a memory array, for selecting one or more word lines and bit lines within selected array blocks, for conveying data information to and from selected memory cells within selected array blocks, and for conveying unselected bias conditions to unselected array blocks.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application discloses subject matter that is also disclosed in thefollowing co-pending U.S. patent applications, each filed on even dateherewith, and each of which is hereby incorporated by reference in itsentirety:

U.S. application Ser. No. ______ (Attorney Docket No. 023-0048) entitled“Passive Element Memory Array Incorporating Reversible Polarity WordLine and Bit Line Decoders” by Luca G. Fasoli, Christopher J. Petti, andRoy E. Scheuerlein;

U.S. application Ser. No. ______ (Attorney Docket No. 023-0051) entitled“Dual Data-Dependent Busses for Coupling Read/Write Circuits to a MemoryArray” by Roy E. Scheuerlein and Luca G. Fasoli;

U.S. application Ser. No. ______ (Attorney Docket No. 023-0056) entitled“Method for Using Dual Data-Dependent Busses for Coupling Read/WriteCircuits to a Memory Array” by Roy E. Scheuerlein and Luca G. Fasoli;

U.S. application Ser. No. ______ (Attorney Docket No. 023-0052) entitled“Memory Array Incorporating Two Data Busses for Memory Array BlockSelection” by Roy E. Scheuerlein, Luca G. Fasoli, and Christopher J.Petti;

U.S. application Ser. No. ______ (Attorney Docket No. 023-0057) entitled“Method for Using Two Data Busses for Memory Array Block Selection” byRoy E. Scheuerlein, Luca G. Fasoli, and Christopher J. Petti;

U.S. application Ser. No. ______ (Attorney Docket No. 023-0053) entitled“Hierarchical Bit Line Bias Bus for Block Selectable Memory Array” byRoy E. Scheuerlein and Luca G. Fasoli; and

U.S. application Ser. No. ______ (Attorney Docket No. 023-0058) entitled“Method for Using a Hierarchical Bit Line Bias Bus for Block SelectableMemory Array” by Roy E. Scheuerlein and Luca G. Fasoli.

BACKGROUND

1. Field of the Invention

The present invention relates to programmable memory arrays, andparticularly semiconductor integrated circuit memory arraysincorporating passive element memory cells, and even more particularly athree-dimensional memory array incorporating such memory cells.

2. Description of the Related Art

Certain passive element memory cells exhibit re-writablecharacteristics. For example, in certain memory cells programming may beachieved by forwarding biasing the memory cell (e.g., with reference tothe polarity of a diode therewithin) with a voltage of approximately6-8V, while erase may be achieved by reverse biasing the memory cellwith a voltage of approximately 10-14V. These high voltages require useof special high voltage CMOS transistors within the word line and bitline decoders. These high-voltage transistors do not scale well as thememory cell word line and bit line pitch decreases. This is particularlyproblematic for 3D memory technology, in which the sheer density of wordlines and bit lines exiting the array, and which must be interfaced witha word line and bit line driver, makes even more important the abilityto provide decoder circuits, and particularly the word line and bit linedriver circuits, compatible with ever smaller array line pitches, yetcapable of impressing a sufficiently high voltage across a selectedmemory cell.

SUMMARY

In general, the invention is directed to a method for using a passiveelement memory array incorporating reversible polarity word line and bitline decoders. However, the invention is defined by the appended claims,and nothing in this section shall be taken as limiting those claims.

In one aspect, the invention provides a method for operating anintegrated circuit memory array having a cross-point array of passiveelement memory cells, each coupled between an associated word line andan associated bit line. The method includes, in a first mode ofoperation, biasing selected word lines at a lower voltage thanunselected word lines, and biasing selected bit lines at a highervoltage than unselected bit lines, and in a second mode of operation,biasing selected word lines at a higher voltage than unselected wordlines, and biasing selected bit lines at a lower voltage than unselectedbit lines.

In another aspect, the invention provides a method for operating anintegrated circuit memory array having a plurality of bit lines on afirst bit line layer and having a plurality of word lines on a firstword line layer. The memory array includes a cross-point array ofpassive element memory cells, each memory cell coupled between anassociated word line and an associated bit line. The method includesselecting one or more word lines using a word line decoder circuithaving a reversible polarity between two modes of operation. The wordline decoder circuit sources a current through a selected passiveelement memory cell in one of the two modes of operation, and sinks acurrent through the selected passive element memory cell in the other ofthe two modes of operation.

In yet another aspect, the invention provides a method for making amemory product. The method includes forming a memory array having aplurality of bit lines on a first bit line layer and having a pluralityof word lines on a first word line layer, said memory array including across-point array of passive element memory cells, each memory cellcoupled between an associated word line and an associated bit line. Themethod also includes forming a word line decoder circuit for selectingone or more word lines, said word line decoder circuit having areversible polarity between two modes of operation. The word linedecoder circuit sources a current through a selected passive elementmemory cell in one of the two modes of operation, and sinks a currentthrough the selected passive element memory cell in the other of the twomodes of operation.

The invention in several aspects is suitable for integrated circuitshaving a memory array, for methods for operating such integratedcircuits and memory arrays, for methods of making memory productsincorporating such arrays, and for computer readable media encodings ofsuch integrated circuits, products, or memory arrays, all as describedherein in greater detail and as set forth in the appended claims. Thedescribed techniques, structures, and methods may be used alone or incombination with one another.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail. Consequently,those skilled in the art will appreciate that the foregoing summary isillustrative only and that it is not intended to be in any way limitingof the invention. Other aspects, inventive features, and advantages ofthe present invention, as defined solely by the claims, may be apparentfrom the detailed description set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings.

FIG. 1 is a schematic diagram of a memory array, illustrating selectedand unselected word lines and bit lines, and exemplary bias conditionsin a forward bias mode of operation.

FIG. 2 is a schematic diagram of the memory array depicted in FIG. 1,but illustrating exemplary bias conditions in a reverse bias mode ofoperation.

FIG. 3 is a schematic diagram of a word line decoder circuit, includingexemplary conditions in a forward bias mode of operation.

FIG. 4 is a schematic diagram of a word line decoder circuit, includingexemplary conditions in a reverse bias mode of operation.

FIG. 5 is a schematic diagram of a bit line decoder circuit, includingexemplary conditions in a forward bias mode of operation.

FIG. 6 is a schematic diagram of a bit line decoder circuit, includingexemplary conditions in a reverse bias mode of operation.

FIG. 7 is a schematic diagram of a word line decoder circuit, includingexemplary conditions in a reverse bias mode of operation for certainother embodiments.

FIG. 8 is a schematic diagram of a bit line decoder circuit, includingexemplary conditions in a reverse bias mode of operation for certainother embodiments.

FIG. 9 is a schematic diagram of a word line decoder circuit having dualdecoded source selection busses, including exemplary conditions in areverse bias mode of operation useful for reset programming.

FIG. 10 is a schematic diagram of a bit line decoder circuit having dualdata-dependent source selection busses, including exemplary conditionsin a reverse bias mode of operation useful for reset programming.

FIG. 11 is a block diagram depicting an exemplary integrated circuitincluding a three-dimensional memory array, and which integrated circuitincludes a global row decoder on one side of the array, and a pair ofcolumn decoders on both top and bottom of the array.

FIG. 12 is a top view representing a word line layer and a bit linelayer of a three-dimensional memory array in accordance with certainembodiments of the present invention, which shows 2:1 interleaved wordline segments, where vertical connections to half of the word linesegments for a block are on the left side of the block, and verticalconnections to the other half of the word line segments for the blockare on the right side of the block. In addition, a word line segmentfrom two adjacent blocks shares each vertical connection.

FIG. 13 is a three-dimensional view depicting a portion of athree-dimensional memory array, consistent with certain embodiments ofthat illustrated in FIG. 12, and illustrating a word line driver circuitcoupled by way of a vertical connection to a respective word linesegment in each of two adjacent array blocks, and on each of two or moreword line layers.

FIG. 14 is a block diagram of a memory array, illustrating two memorystripes, each having two (or more) memory bays, and each bay including aplurality of memory array blocks. Two array blocks are shown as beingsimultaneously selected, each coupling its respective bit lines to arespective one of two data busses associated with the memory bay.

FIG. 15 is a block diagram of a memory bay, illustrating anotherarrangement in which two array blocks are shown as being simultaneouslyselected, each coupling its respective bit lines to a respective one oftwo data busses associated with the memory bay.

FIG. 16 is a block diagram of a memory bay, illustrating anotherarrangement in which two array blocks are shown as being simultaneouslyselected, each coupling its respective bit lines to a respective one oftwo data busses associated with the memory bay.

FIG. 17 is a block diagram of a memory bay, illustrating anotherarrangement in which two array blocks are shown as being simultaneouslyselected, each coupling its respective bit lines to a respective one oftwo data busses associated with the memory bay, which busses aredisposed on the same side of the memory array blocks.

FIG. 18 is a block diagram of a memory bay, illustrating anotherarrangement in which two non-adjacent array blocks are shown as beingsimultaneously selected, each coupling its respective bit lines to arespective one of two data busses associated with the memory bay.

FIG. 19 is a block diagram of a portion of a memory bay, illustrating anexemplary hierarchical decoding arrangement for providing appropriateconditions on the source selection busses for the selected andunselected array blocks.

FIG. 20 is a block diagram of a portion of a memory bay, illustratinganother exemplary hierarchical decoding arrangement for providingappropriate conditions on the source selection busses for the selectedand unselected array blocks.

FIG. 21 is a block diagram of a portion of a memory bay, illustratinganother exemplary hierarchical decoding arrangement for providingappropriate conditions on the source selection busses for the selectedand unselected array blocks.

FIG. 22 is a block diagram of a portion of a memory bay, illustratinganother exemplary hierarchical decoding arrangement for providingappropriate conditions on the source selection busses for the selectedand unselected array blocks.

FIG. 23 is a block diagram of a data circuit, including a read senseamplifier, a set driver, and a reset driver useful for variousembodiments described herein.

FIG. 24 is a block diagram of an exemplary reset circuit, including adepiction of the reset path through a selected memory cell and the wordline and bit line selection paths.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 1 is a schematic diagram of an exemplary passive element memoryarray 100. Two word lines 102, 104 are shown, as well as two bit lines106, 108. Word line 102 is assumed to be a selected word line (SWL), andword line 104 is assumed to be an unselected word line (UWL). Similarly,bit line 106 is assumed to be a selected bit line (SBL), and bit line108 is assumed to be an unselected bit line (UBL). Four passive elementmemory cells 101, 103, 105, 107 are shown, each coupled between anassociated word line and an associated bit line.

Memory cell 101 is associated with the selected word line 102 and theselected bit line 106, and may be viewed as an “S” cell (i.e.,“selected” cell). Memory cell 103 is associated with the unselected wordline 104 and the selected bit line 106, and may be viewed as an “F” cell(i.e., “off” cell). Memory cell 105 is associated with the selected wordline 102 and the unselected bit line 108, and may be viewed as an “H”cell (i.e., “half-selected” cell). Lastly, memory cell 107 is associatedwith the unselected word line 104 and the unselected bit line 108, andmay be viewed as a “U” cell (i.e., “unselected” cell).

Also illustrating in FIG. 1 are exemplary biasing conditions for aforward bias mode of operation. As described elsewhere herein, such aforward bias mode may be used for a programming mode, a block erasemode, and a read mode (although usually with different voltage levels orconditions for such different modes). As shown, the bias conditions maybe viewed as appropriate for a programming mode of operation for aselected array block, and will be described as such.

The selected word line 102 is biased at a VSX voltage (e.g., ground),the selected bit line 106 biased at a VSB voltage (e.g., +8 volts), theunselected word line 104 is biased at a VUX voltage (e.g., +7.3 volts),and the unselected bit line 108 biased at a VUB voltage (e.g., +0.7volts). The selected bit line bias voltage VSB may be viewed as theprogramming voltage VPP, as substantially this entire voltage isimpressed across the selected memory cell 101 (since the selected wordline is biased at ground), less certain resistive drops in the bussesand array lines themselves. The unselected bit line bias voltage VUB isalso preferably set at a value corresponding to an apparent “thresholdvoltage” in a forward biased direction of each memory cell, and is thusshown as a voltage VT being impressed on the unselected bit line 108.Similarly, the unselected word line bias voltage VUX is also preferablyset at a value of VPP−VT.

Under these biasing conditions, the S cell 101 receives a forward biasvoltage equal to VPP (e.g., +8 volts), the F cell 103 receives a forwardbias voltage equal to VT (e.g., +0.7 volts), the H cell 105 receives aforward bias voltage equal to VT (e.g., +0.7 volts), and the U cell 107receives a reverse bias voltage equal to VPP−2VT (e.g., −6.6 volts).There are several exemplary memory cell technologies that, when biasedunder these conditions, the selected cell will be changed to a lowervalue of resistance, while the F, H, and U cells will not appreciablychange in resistance. Exemplary cells are described herebelow.

Referring now to FIG. 2, exemplary biasing conditions 200 are shown fora reverse bias mode of operation. As described elsewhere herein, such areverse bias mode may be used for a programming mode or a block erasemode (although usually with different conditions for such differentmodes). As shown, the bias conditions may be viewed as appropriate foreither a programming mode or erase mode of operation for a selectedarray block, and will be described as such.

Each of the bias conditions VSX, VUX, VSB, and VUB are now redefined forvalues appropriate for the present mode of operation. The selected wordline 102 is biased at a VSX voltage of VRR/2 (e.g., +5 volts), and theselected bit line 106 biased at a VSB voltage of −VRR/2 (e.g., −5volts). The unselected word line voltage VUX and the unselected bit linevoltage VUB are both ground.

Under these biasing conditions, the S cell 101 receives a reverse biasvoltage equal in magnitude to VRR (e.g., −10 volts), the F cell 103receives a reverse bias voltage equal to VRR/2 (e.g., −5 volts), and theH cell 105 receives a reverse bias voltage equal to VRR/2 (e.g., −5volts). Of note, the U cell 107 receives no bias across the cell.

There are several exemplary memory cell technologies (referenced below)that, when biased under these conditions, the selected cell will bechanged from a lower value of resistance to a higher value ofresistance, while the F, H, and U cells will not appreciably change inresistance. It should also be noted that the unselected U memory cells,which otherwise may support a considerable amount of leakage currentwhen biased with several volts across such a cell, have no bias andtherefore no leakage current. As will be described in further detail,many useful memory array embodiments include a far larger number of Ucells than H cells of F cells, and such arrays will have significantlyless leakage current in the unselected memory cells of the array, andhence much less power dissipation, than with other biasing schemes.

By “splitting” the VRR voltage in this reverse mode, and biasing the SBLat a negative voltage equal to one half of the programming voltage, andbiasing the SWL at a positive voltage equal to one half of theprogramming voltage, the voltage requirements of both the bit linedecoder and the word line decoder are significantly relaxed.Consequently, consistent with the small pitch of the array lines (e.g.,word lines and bit lines), the high voltage transistors in the arrayline driver circuits take up less area because they may be designed fora relatively lower “split” voltage.

Other memory technologies have faced similar issues regarding theprogramming and erase voltages (and the area needed for suchhigh-voltage transistors) not scaling at the same rate as the memorycell pitch. For example, the impact of this issue in FLASH memory issomewhat reduced because of the larger fanout of typical FLASH-basedmemory arrays. The more space consuming design rules for high voltagetransistors can be ammortized in some newer technologies by increasingthe memory block size. However, in a diode-based passive element memoryarray, larger block size comes at a cost of increased leakage throughthe unselected memory cells belonging to the selected array. By biasingsuch unselected memory cells as described in FIG. 2, this leakagecomponent can be reduced to almost zero, and a larger block sizesachieved with little deleterious power dissipation.

Referring now to FIG. 3, an exemplary word line decoder circuit isshown, including showing bias conditions suitable for the forward biasmode of operation (as described in FIG. 1). A row decoder circuit isshown on the left side of the page, which shows two decoded outputs 158,162. The decoded output 158 corresponds to a selected decoded output,while the decoded output 162 corresponds to an unselected decodedoutput. A row decoder 152, which may be implemented using any of avariety of well-known techniques, generates a plurality of decodedoutputs, such as output 155, 159, which are conditionally inverted bythe multiplexers 157, 161, and the inverters 156, 160. An invertingbuffer is incorporated after the NAND gate to drive node 155 due to thelarge capacitive loading on node 158 (i.e., in the event, as here, thatmultiplexer 157 steers node 155 to the output 158). The row decoder 152is operated in this mode of operation with an upper supply voltage equalto VPP coupled to power supply node 153, and a lower supply voltage ofground coupled to power supply node 154. In this mode of operation, therow decoder is an “active high” decoder, meaning that the selectedoutput (or outputs), such as decoded output node 158, is driven to thehigher of two available voltage states, which in this case is VPP. Theunselected decoded outputs, such as decoded output node 162, are drivento the lower of the two available voltage states, which in this case isground. The description that follows will initially assume that only onesuch decoded output node is selected (e.g., “high”) at a time.

Each of decoded output is coupled to one or more word line drivercircuits. For example, decoded output node 158 is coupled to a word linedriver circuit which includes PMOS transistor 171 and NMOS transistor172. The respective drain terminal of transistors 171, 172 are bothcoupled to a word line, in this case representing the selected word line102. While certain embodiments of this invention contemplate decodersother than multi-headed decoders, FIG. 3 depicts a second word linedriver circuit also coupled to the decoded output node 158, whichrepresents one or more remaining word line driver circuits associatedwith this particular decoded output node 158. This second word linedriver circuit includes PMOS transistor 173 and NMOS transistor 174, theoutput of which drives a word line 181 which represents one or morehalf-selected word lines.

The respective source terminals of the NMOS transistors in each of theseword line driver circuits is coupled to a respective bus line of asource selection bus XSEL. In this mode of operation, the sourceselection bus is decoded, based upon address information, so that onesuch a bus line is biased at active state suitable for a word line forthis mode of operation, while the remaining bus lines are biased at aninactive state suitable for word lines for this mode of operation. Incertain embodiments, more than one such source selection bus line may beactive, but we shall for now assume that the bus line 167 is active, andis biased at ground, while one or more remaining bus lines, representedby bus line 168, are inactive and are driven to the unselected word linevoltage VUX (shown as VPP−VT).

Since the voltage on decoded output node 158 (VPP) is higher than thevoltage of bus lines 167, 168, both of the NMOS transistors 172, 174 areturned on, thus driving the selected word line 102 to ground, anddriving the half selected word line 181 to VPP−VT. These two conductionpaths are indicated by the open arrowhead lines.

The respective source terminals of the PMOS transistors in each of theseword line driver circuits is coupled to an unselected bias line UXL,also labeled node 164. In this mode of operation, the UXL bias lineconveys the unselected word line voltage VUX. Since the voltage ondecoded output node 158 (VPP) is higher than the voltage of the UXL biasline, both PMOS transistors 171, 173 are turned off.

The decoded output node 162 is coupled to a word line driver circuitwhich includes PMOS transistor 175 and NMOS transistor 176. Therespective drain terminal of transistors 175, 176 are both coupled to aword line, in this case representing the unselected word line 104. Asecond word line driver circuit also coupled to the decoded output node162 represents one or more remaining word line driver circuitsassociated with the decoded output node 162, and includes PMOStransistor 177 and NMOS transistor 178, the output of which drives anunselected word line 183.

As before, the respective source terminals of the NMOS transistors ineach of these word line driver circuits is coupled to a respective busline of a source selection bus XSEL. Since the voltage on decoded outputnode 162 (ground) is at or lower than the voltage of bus lines 167, 168,both of the NMOS transistors 176, 178 are turned off. The respectivesource terminals of the PMOS transistors in each of these word linedriver circuits is coupled to the unselected bias line UXL node 164.Since the voltage on decoded output node 162 (ground) is lower than thevoltage of the UXL bias line 164 (by more than the PMOS thresholdvoltage), both PMOS transistors 175, 177 are turned on, thus driving theunselected word lines 104, 183 to VUX (e.g., VPP−VT). These twoconduction paths are indicated by the open arrowhead lines.

Referring now to FIG. 4, this same exemplary word line decoder circuitis shown including bias conditions suitable for the reverse bias mode ofoperation (as described in FIG. 2). The decoded output 158 of the rowdecoder circuit still corresponds to a selected decoded output, whilethe decoded output 162 corresponds to an unselected decoded output. Therow decoder 152 is operated in this mode of operation with an uppersupply voltage equal to VRR/2 coupled to power supply node 153, and alower supply voltage of ground coupled to power supply node 154. In thismode of operation, the row decoder is an “active low” decoder, and theactive (selected) decoded output 158 is driven to the lower of twoavailable voltage states, which in this case is GND (ground), usinginverter 156 and multiplexer 157. The unselected decoded outputs, suchas decoded output node 162, are now driven to the higher of the twoavailable voltage states, which in this case is VRR/2, using inverter160 and multiplexer 161.

In this mode of operation, for the exemplary embodiment described, theindividual bus lines of source selection bus XSEL are all driven to thesame of bias condition, being ground, and the “unselected” bias line UXLconveys a bias voltage equal to VRR/2 (e.g., +5 volts). In this reversemode of operation, the bias line UXL actually conveys an active statesuitable for word lines, rather than an inactive or unselected biascondition. Since the voltage on decoded output node 158 (GND) isconsiderably lower than the voltage of the bias line UXL (i.e., by morethan a PMOS threshold voltage), both of the PMOS transistors 171, 173are turned on, thus driving the selected word line 102 to VRR/2, anddriving the what would have been the half-selected word line (shown hereas selected word line 181) also to VRR/2. These two conduction paths areindicated by the open arrowhead lines.

In this mode of operation the source selection bus XSEL is not decoded,and each such bus line is biased at an inactive state suitable for aword line (e.g., ground). Since the voltage on decoded output node 158(ground) is no higher than the voltage of bus lines 167, 168, both ofthe NMOS transistors 172, 174 are turned off.

The decoded output node 162, which is an unselected output, is driven toVRR/2 by inverter 160 and multiplexer 161. Since the voltage on decodedoutput node 162 higher than the voltage of bus lines 167, 168, both ofthe NMOS transistors 176, 178 are turned on, thus driving the unselectedword lines 104, 183 to ground. These two conduction paths are indicatedby the open arrowhead lines. Since the voltage on decoded output node162 is the same as the voltage conveyed on the UXL bias line 164, bothPMOS transistors 175, 177 are turned off.

Referring now to FIG. 5, an exemplary bit line decoder circuit is shown,including showing bias conditions suitable for the forward bias mode ofoperation (as described in FIG. 1). A column decoder circuit is shown onthe left side of the page, which shows two decoded outputs 208, 212. Thedecoded output 208 corresponds to a selected decoded output, while thedecoded output 212 corresponds to an unselected decoded output. A columndecoder 202, which may be implemented using any of a variety ofwell-known techniques, generates a plurality of decoded outputs, such asoutput 205, 209, which are conditionally inverted by the multiplexers207, 211, and the inverters 206, 210. Unlike the row decoder, there isno inverting buffer after the NAND gate to drive node 205 because thecapacitive loading on node 208 is much lower than for the row decoderoutputs. The column decoder 202 is operated in this mode of operationwith an upper supply voltage equal to VPP coupled to power supply node203, and a lower supply voltage of ground coupled to power supply node204. In this mode of operation, the column decoder is an “active low”decoder. The unselected decoded outputs, such as decoded output node212, are driven to the higher of the two available voltage states, whichin this case is VPP. The description that follows will initially assumethat only one such decoded output node 208 is selected (e.g., “low”) ata time.

Each of the decoded outputs is coupled to one or more bit line drivercircuits. For example, decoded output node 208 is coupled to a bit linedriver circuit which includes PMOS transistor 221 and NMOS transistor222. The respective drain terminal of transistors 221, 222 are bothcoupled to a bit line, in this case representing the selected bit line106. While certain embodiments of this invention contemplate decodersother than multi-headed decoders, FIG. 5 depicts a second bit linedriver circuit also coupled to the decoded output node 208, whichrepresents one or more remaining bit line driver circuits associatedwith this particular decoded output node 208. This second word linedriver circuit includes PMOS transistor 223 and NMOS transistor 224, theoutput of which drives a bit line 231 which represents one or morehalf-selected bit lines. In contrast to the word line decoder, such ahalf selected bit line may represent a selected bit line which is beingmaintained in an inactive state.

The respective source terminals of the PMOS transistors in each of thesebit line driver circuits is coupled to a respective bus line of a sourceselection bus SELB. In this mode of operation, the source selection busSELB is data dependent, and may further be decoded based upon addressinformation, so that one or more such bus lines are biased at activestate suitable for a bit line for this mode of operation, while theremaining bus lines are biased at an inactive state suitable for bitlines for this mode of operation. In certain embodiments, more than onesuch source selection bus line may be active, but we shall for nowassume that the bus line 217 is active, and is biased at VPP, while oneor more remaining bus lines, represented by bus line 218, are inactiveand are driven to the unselected bit line voltage VUB (shown as VT).

Since the voltage on decoded output node 208 (ground) is lower than thevoltage of bus lines 217, 218, both of the PMOS transistors 221, 223 areturned on, thus driving the selected bit line 106 to VPP, and drivingthe half selected bit line 231 to VT. These two conduction paths areindicated by the open arrowhead lines.

The respective source terminals of the NMOS transistors in each of thesebit line driver circuits is coupled to an unselected bias line UYL, alsolabeled node 214. In this mode of operation, the UYL bias line conveysthe unselected bit line voltage VUB. Since the voltage on decoded outputnode 208 (ground) is lower than the voltage of the UYL bias line, bothNMOS transistors 222, 224 are turned off.

The decoded output node 212 is coupled to a bit line driver circuitwhich includes PMOS transistor 225 and NMOS transistor 226. Therespective drain terminal of transistors 225, 226 are both coupled to abit line, in this case representing the unselected bit line 108. Asecond bit line driver circuit also coupled to the decoded output node212 represents one or more remaining bit line driver circuits associatedwith the decoded output node 212, and includes PMOS transistor 227 andNMOS transistor 228, the output of which drives an unselected word line233.

As before, the respective source terminals of the PMOS transistors ineach of these bit line driver circuits is coupled to a respective busline of a source selection bus SELB. Since the voltage on decoded outputnode 212 (VPP) is at the voltage of bus lines 217, 218, both of the PMOStransistors 225, 227 are turned off. The respective source terminals ofthe NMOS transistors in each of these bit line driver circuits iscoupled to the unselected bias line UYL node 214. Since the voltage ondecoded output node 212 is VPP, both NMOS transistors 226, 228 areturned on, thus driving the unselected bit lines 108, 233 to VUB (e.g.,VT). These two conduction paths are indicated by the open arrowheadlines.

Referring now to FIG. 6, the bit line decoder circuit is shown includingbias conditions suitable for the reverse bias mode of operation (asdescribed in FIG. 2). The decoded output 208 of the column decodercircuit still corresponds to a selected decoded output, while thedecoded output 212 corresponds to an unselected decoded output. Thecolumn decoder 202 is operated in this mode with an upper supply voltageequal to GND coupled to power supply node 203, and a lower supplyvoltage of −VRR/2 coupled to power supply node 204. In this mode ofoperation, the column decoder is an “active high” decoder, and theactive (selected) decoded output 208 is driven to the higher of twoavailable voltage states, which in this case is GND (ground), byinverter 206 and multiplexer 207. The unselected decoded outputs, suchas decoded output node 212, are now driven to the lower of the twoavailable voltage states, which in this case is −VRR/2, by inverter 210and multiplexer 211.

In this mode of operation, for the exemplary embodiment described, theindividual bus lines of source selection bus SELB are all driven to thesame of bias condition, being ground, and the “unselected” bias line UYLconveys a bias voltage equal to −VRR/2 (e.g., −5 volts). In this reversemode of operation, the bias line UYL actually conveys an active statesuitable for bit lines, rather than an inactive or unselected biascondition. Since the voltage on decoded output node 208 (ground) isconsiderably higher than the voltage of the bias line UYL (i.e., by morethan a NMOS threshold voltage), both of the NMOS transistors 222, 224are turned on, thus driving the selected bit line 106 to −VRR/2, anddriving the what would have been the half-selected bit line (shown hereas selected bit line 231) also to −VRR/2. These two conduction paths areindicated by the open arrowhead lines.

In this mode of operation the source selection bus SELB is notdata-dependent nor decoded (at least within a given block), and eachsuch bus line is biased at an inactive state suitable for a bit line(e.g., ground). and both of the PMOS transistors 221, 223 are turnedoff.

The decoded output node 212 is an unselected output and is driven to−VRR/2. Both of the PMOS transistors 225, 227 are turned on, thusdriving the unselected bit lines 108, 233 to ground. These twoconduction paths are indicated by the open arrowhead lines. Both NMOStransistors 226, 228 are turned off.

It should be noted that, in the forward mode, the column decoder isactive low and the bit lines are active high. But in the reverse mode,the column decoder reverses its polarity and becomes active high, whilethe bit lines themselves also reverse polarity and become active low.Conversely, in the forward mode, the row decoder is active high and theword lines are active low. But in the reverse mode, the row decoderreverses its polarity and becomes active low, while the word linesthemselves also reverse polarity and become active high. It should alsobe noted that the column decoder output levels shift in average voltagebetween the forward mode (i.e., GND to VPP) and reverse mode (i.e.,−VRR/2 to GND).

When viewed as a non-multi-headed decoder (in FIGS. 3, 4, 5, and 6, onlythe non-dashed array line driver circuits), the operation of the decodercircuit may be described very simply. In the reverse mode, the word linedecoder reverses its polarity and brings one selected word line high(˜5V) and keeps all others at ground. The converse happens on the bitline selection side, where one bit line is selected and brought to −5Vand all others are grounded. The end result is 10V of reverse biasacross the selected memory cell and zero across the others. Thetransistors in the word line and bit line driver circuits only have towithstand 5V, or half the maximum voltage, rather than the entirevoltage.

When one considers the implications of using multi-headed decoders (inFIGS. 3, 4, 5, and 6, including the dashed array line driver circuits),it should be noted that the circuits thus far described utilize adecoded source selection bus in the forward direction, which allows asingle one of the group of array lines to be selected (while theremaining half-selected array lines are nonetheless driven to anunselected bias condition. However, in the reverse mode, the selecteddecoded output from the row and column decoder couples each array lineto a single unselected bias line, such as UXL and UYL. Achievinghalf-selected array lines in the reverse mode is not possible with asingle bias line. As a result, the above circuits and techniques arehighly useful when arranged to select a block of array lines in thereverse mode, such as a “block erase”. As can be seen in FIGS. 4 and 6,a block of selected word lines and a block of selected bit lines aresimultaneously selected in the reverse mode, with no independentlyconfigurable half-selected array lines. Such a block operation avoidsaltogether any need for half-selected lines. The decoding implicationscan be very similar to that disclosed in U.S. Pat. No. 6,879,505 to RoyE. Scheuerlein, entitled “Word Line Arrangement Having Multi-Layer WordLine Segments for Three-Dimensional Memory Array”, the disclosure ofwhich is hereby incorporated by reference in its entirety. Whether sucha block operation may be configured (or how large a block may beconfigured) largely rests upon the magnitude of the cell reset current,the number of cells conducting such reset current simultaneously, andwhether the PMOS and NMOS transistors within the word line drivercircuit and the bit line driver circuit can support such current withacceptable voltage drop.

Half-selected array lines may be provided in the reverse mode (inaddition to that already provided in the forward mode) by using othertechniques. In a first such technique, the row and column decoders maybe powered by over-voltages, so that the decoded output nodes traversehigher than the PMOS source voltage and lower than the NMOS sourcevoltage. By so doing, the selected word line may be driven up to the+VRR/2 voltage through the NMOS transistor, and the selected bit linemay be driven down to the −VRR/2 voltage through the PMOS transistor.This utilizes the same transistors to drive the selected word line andbit line as during the forward mode.

Such a technique is illustrated in FIGS. 7 and 8. Referring initially toFIG. 7, a word line decoder circuit is illustrated which utilizes anoverdriven decoded output to drive the array line drivers, whose sourcesremain at the bias conditions described above. In this row decodercircuit, the row decoder 152 is powered by an 8 volt upper supplyvoltage and a negative 1 volt lower supply voltage. The polarity of thedecoded output nodes 158, 162 is reversed relative to that shown in FIG.4, and is now an active high decoder providing a selected output 158 at+8 volts and an unselected decoded output node 162 at −1 volt. Thesource selection bus XSEL remains a decoded bus. One (or more) of itsindividual bus lines is selected and driven to +5 volts, while theunselected bus lines are driven to ground. The NMOS transistor 172 isturned on, and conducts the selected word line 102 to the associatedXSEL bus line voltage (+5 volts). The NMOS transistor 174 is also turnedon, and conducts the half-selected word line(s) 181 to ground. With theunselected decoded output node 162 at −1 volt, the PMOS transistors 175,177 are both turned on, and conduct the unselected word lines 104, 183to ground. In some embodiments utilizing this technique, the conditionaloutput inverters 156, 160 and the multiplexers 157, 161 (shown here as“dashed”) are not used.

Referring now to FIG. 8, a bit line decoder circuit is illustrated whichalso utilizes an overdriven decoded output to drive the array linedrivers. In this column decoder circuit, the column decoder 202 ispowered by a +1 volt upper supply voltage and a negative 8 volt lowersupply voltage. The polarity of the decoded output nodes 208, 212 isreversed relative to that shown in FIG. 6, and is now an active lowdecoder providing a selected output 208 at −8 volts and an unselecteddecoded output node 212 at +1 volt. One (or more) of the individual SELBbus lines 217 is selected an driven to −5 volts, while the unselectedSELB bus lines 218 are driven to ground. The PMOS transistor 221 isturned on, and conducts the selected bit line 106 to the associated SELBbus line voltage (−5 volts). The PMOS transistor 223 is also turned on,and conducts the half-selected bit line(s) 231 to ground. With theunselected decoded output node 212 at +1 volt, the NMOS transistors 226,228 are both turned on, and conduct the unselected bit lines 108, 233 toground. In some embodiments utilizing this technique, the conditionaloutput inverters 206, 210 and the multiplexers 207, 211 are not used.

In another technique, half-selected word lines and bit lines may beprovided in the reverse mode by incorporating a respective reversesource selection bus in place of the single unselected bias lines UXLand UYL. Referring now to FIG. 9, a word line decoder circuit isillustrated which utilizes dual decoded source selection busses. Areverse source selection bus XSELP for the PMOS transistors of the wordline driver circuits has been incorporated in place of the unselectedbias line UXL shown in FIG. 4. The remainder of this word line decodercircuit operates as before.

In the reverse mode, the selected decoded output node 158 is active lowand driven to ground. A selected one of the individual bus lines of thereverse source selection bus XSELP is biased to an active bias conditionsuitable for the reverse mode of operation for a word line. In thiscase, the selected bus line 243 of the XSELP bus is driven to VRR/2, andthe unselected bias lines 244 of the XSELP bus are driven to an inactivebias condition suitable for this mode of operation for word lines, inthis case being driven to ground. The PMOS transistor 171 is turned onby the low voltage coupled to its gate, and drives the selected wordline 102 to the VRR/2 potential. However the PMOS transistor 173 withinthe half-selected word line driver circuit remains off because thevoltage on its gate is not low enough relative to its source, since bothare at ground.

Since the NMOS transistor 174 is also turned off, neither transistorwithin the half-selected word line driver circuit is turned on.Consequently, the half selected word lines float at or near the groundpotential. This occurs if, as is the case in this exemplary circuit, theNMOS pull-down transistor 174 is larger than the PMOS pull-up transistor173. The larger transistor has a greater amount of leakage to itssubstrate well than does the smaller transistor. Consequently, sincetransistor 174 has a substrate tied to ground, the leakage current toground dominates over the substrate leakage current to VRR/2 resultingfrom the PMOS transistor 173, and this net current tends to maintain thehalf-selected word lines 181 at or near the ground potential. The wordline driver circuits associated with unselected decoded output nodes 162operate as before, with the NMOS transistors 176, 178 being turned on toconduct the unselected word lines 104, 183 to ground.

In an alternative embodiment, the low level of the decoded output nodes158, 162 may be driven below ground (e.g., to a voltage at or below thePMOS threshold voltage below ground, i.e., −VTP) by operating the rowdecoder 152, inverters 156, 160 and multiplexers 157, 161 using a lowerpower supply 154 equal to −VTP (or lower). As a result, the PMOS pull-uptransistor 173 is turned on to actively drive the half-selected wordline(s) 181 to ground.

An analogous situation occurs in a column decoder circuit incorporatingdual data-dependent source selection busses. Referring now to FIG. 10, abit line decoder circuit is illustrated which utilizes dual decoded (inthis cases data-dependent) source selection busses. A reverse sourceselection bus SELN for the NMOS transistors of the bit line drivercircuits has been incorporated in place of the unselected bias line UYLshown in FIG. 6. The remainder of this bit line decoder circuit operatesas before.

In the reverse mode, the selected decoded output node 208 is active highand driven to ground. A selected one of the individual bus lines of thereverse source selection bus SELN is biased to an active bias conditionsuitable for the reverse mode of operation for a bit line. In this case,the selected bus line 247 of the SELN bus is driven to −VRR/2, and theunselected bias lines 248 of the SELN bus are driven to an inactive biascondition suitable for bit lines for this mode of operation, in thiscase being driven to ground. The NMOS transistor 222 is turned on by thehigh voltage coupled to its gate, and drives the selected bit line 106to the −VRR/2 potential. However the NMOS transistor 224 within thehalf-selected bit line driver circuit remains off because the voltage onits gate is not high enough relative to its source, since both are atground.

Since the PMOS transistor 223 is also turned off, neither transistorwithin the half-selected bit line driver circuit is turned on.Consequently, the half selected bit lines float at or near the groundpotential. This occurs if, as is the case in this exemplary circuit, thePMOS pull-p transistor 223 is larger than the NMOS pull-down transistor224. The larger transistor will have a greater amount of leakage to itssubstrate well than does the smaller transistor. Consequently since thelarger transistor 223 has a substrate tied to ground, the leakagecurrent to ground dominates over the substrate leakage current to −VRR/2resulting from the NMOS transistor 224, and this net current tends tomaintain the half-selected bit lines 231 at or near the groundpotential. The bit line driver circuits associated with unselecteddecoded output nodes 212 operate as before, with the PMOS transistors225, 227 being turned on to conduct the unselected bit lines 108, 233 toground.

For both of the decoder circuits, operation in the forward mode proceedssubstantially as indicated in FIGS. 4 and 6. Considering the row decodercase, in the forward mode the source selection bus is decoded, and allunselected word lines are driven to the unselected bias line UXL. In theforward mode using the dual decoded row decoder circuit, the reversesource selection bus is not decoded, and all its individual bus linesare driven to the same voltage as the UXL bus line. Thus, the word linedriver circuits operate unchanged relative to FIG. 4. Rather, a singlebias line UXL has been replaced by a plurality of “bias lines” which areeach driven to the same voltage as the former UXL bias line, and towhich each unselected word line is driven.

In the column decoder case, in the forward mode the source selection busSELB is decoded, and all unselected bit lines are driven to theunselected bias line UYL. In the forward mode using the dual decoded rowdecoder circuit, the reverse source selection bus is not decoded, andall its individual bus lines are driven to the same voltage as the UYLbus line. Thus, the bit line driver circuits operate unchanged relativeto FIG. 6. Rather, a single bias line UYL has been replaced by aplurality of “bias lines” which are each driven to the same voltage asthe former UYL bias line, and to which each unselected bit line isdriven.

The decoder circuits thus far described are useful for implementingmemory arrays in which the memory cells include a reversible resistorplus a diode. Such memory cells maybe reset using a reverse bias appliedacross the cell, and providing for half-selected word lines and bitlines allows individual word lines and bit lines to be placed in a resetbias condition, thus providing the capability to reset individual memorycells without having to reset an entire block.

The technique described in FIGS. 7 and 8 has the advantage of only asingle decoded source selection bus, although since the row and columndecoders are powered by over-voltages, the voltage requirement for suchdecoder circuits is higher. The technique described in FIGS. 9 and 10reduces the voltage requirements by not utilizing over-voltage poweringthe two decoder circuits, at the expense of an additional decoded(and/or data dependent) reverse source selection bus, and the likelyincreased area to incorporate the array line drivers using two decodedsource selection busses. The bit line select circuit has twice as manybus lines, and may be wiring limited. The word line select circuits mayalso be somewhat larger and wiring limited (i.e., the word line drivercircuits include six additional decoded lines for a six-headed decoder,and the PMOS device is slightly larger than earlier circuits).Nonetheless, either technique may be useful over the other forparticular embodiments.

The forward mode was described above in the context of a programmingcondition, in which the voltage applied to the selected bit line is VPP.The forward mode is also applicable for a read mode in which theselected bit line is driven to a read voltage VRD, and the selected wordline again is driven to ground. Such a read voltage may be a much lowervoltage than the programming voltage VPP, and the unselected word linebias voltage VUX and the unselected bit line bias voltage VUBaccordingly reduced over their values for the programming mode.

Certain memory cells may be “programmed” using a forward bias mode, andblock erased using the reverse mode. Other cells may be pre-conditioned(such as during manufacture) using an initial forward bias programmingtechnique, but then are “programmed” using the reverse mode, and“erased” using the forward mode. To avoid confusion with historicalusage in the programmable arts, and to comprehend different memorytechnologies that are contemplated for use with the decoder circuitsthus far described, three different modes of operation are useful todescribe: read, set, and reset. In the read mode, a read voltage VRD isapplied across a selected memory cell. In the set mode, a set voltageVPP is applied across a selected memory cell. In the exemplaryembodiments thus far described, the read voltage VRD and the set voltageVPP are both positive voltages, and such modes are carried out using theforward mode of decoder operation. In the reset mode, a reset voltageVRR is applied across a selected memory cell. In the exemplaryembodiments thus far described, the reset voltage VRR is applied as areverse bias voltage, and is carried out using the reverse mode ofdecoder operation.

The reset mode described above uses a split voltage technique to limitthe voltage requirements for the decoder circuits, and drives a selectedbit line to a negative voltage (i.e., using a triple well semiconductorstructure). Alternatively, the reset mode may be carried out withentirely non-negative voltages. In such a case, the reset voltage VRR isconveyed to the selected word line, and ground conveyed to the selectedbit line. The VUX and VUB voltages are preferably set to approximatelyVRR/2.

Many types of memory cells (described below) are capable of beingprogrammed using the reset mode. In certain of these memory celltechnologies, an antifuse within each memory cell is initially popped inthe forward direction. Then the resistance of each memory cell is“tuned” in the reverse bias direction to accomplish programming. Thiswould be the case for a one-time-programmable cell. For re-writablecells, the cell is erased using the forward direction, which could beperformed in a block of various sizes, and then programmed using thereverse mode.

The reverse bias is used to reset the selected memory cell. Theprogramming current is supplied by a diode breakdown. In addition, thebias conditions associated with such programming may be carefullycontrolled, including controlling the voltage ramp of the selected wordline and/or bit line. Additional insight into useful programmingtechniques maybe found in U.S. Pat. No. 6,952,030 referenced below.Multiple programming operations may be used to program variousresistance states, as described in the 023-0049 and 023-0055applications, referenced below, and as described in more detail in theMA-163-1 application, referenced below. The use of sloped programmingpulses is described in the SAND-01114US0 and SAND-01114US1 applications,referenced below, and techniques for trimming the resistance of multiplecells is described in the SAND-01117US0 and SAND-01117US1 applications,referenced below.

The use of the reset programming as described above, particularly in thecontext of the dual decoded source select lines, for programming apassive element memory cell incorporating a trimmable resistive elementis particularly useful in providing great flexibility to allow for alarger array block size. Even in a selected array block (as all thedescriptions above have assumed), there is no bias across the unselectedmemory cells in the reset mode, and therefore no wasted powerdissipation. The reverse current through a cell (Irev) is not a concernfor block size. Therefore many blocks may be selected to increase thewrite bandwidth. In addition, the voltage across each half selectedmemory cell is only one half of the programming voltage, and is safe forthese cells.

It should be noted that in the descriptions above, the reset modedescribes selected and half-selected word lines and bit lines. In thecontext of row selection, for example, such a half-selected word linemay in fact be “not selected” by a given address, and such term is anartifact of the multi-headed word line driver structure. However, in thecontext of the bit lines, such a half-selected bit line may in fact beselected as far as the column address is concerned, but may be biased toan inactive state rather than the active state for the bit lines, eitherbecause the particular data for that bit line does not require“programming” the cell, or because the bit line is “waiting” to beprogrammed. This occurs when fewer than the number of bit line decoderheads are programmed at the same time. Of note, however, programmingbandwidth concerns suggest configuring a memory array to simultaneouslyprogram as many bit lines as possible.

Triple well processing allows the selected bit line(s) to be taken to anegative voltage while the selected word line(s) is taken to a positivevoltage. In the reset programming (i.e., reverse mode), the referencelevel for all unselected array lines (bit lines and word lines) isground, which allows for rapid decoding and selection of both word linesand bit lines. Referring back to the description of the half-selectedword lines and bit lines being floating at ground (due to the leakagecurrent to the well potential of the larger of the two drivertransistors), the resistive nature of the memory cells provides anadditional leakage current between such half-selected array lines andthe unselected array lines, which are actively held at the unselectedbias level. This further encourages the unselected array lines to remainfloating at or near the unselected bias potential.

Two-dimensional memory arrays are contemplated, but the decoderarrangements are believed particularly useful for a 3D memory arrayhaving multiple memory planes. In certain preferred embodiments, thememory array is configured with each word line comprising word linesegments on each of more than one memory plane, as described below.

FIG. 11 is a block diagram of an exemplary memory array 300. Dual rowdecoders 302, 304 generate row select lines for the array, which eachtraverse across the array 300, as will be described herein. In thisembodiment, the word line driver circuits (not shown) are spatiallydistributed beneath the memory array and make connection to the wordlines by way of vertical connections (one of which is labeled 310) onalternating sides of individual memory array blocks (two which arelabeled 306, 308). The memory array shown includes two memory “stripes”318, 320, and further includes four column decoder and bit line circuitblocks 312, 314, 316 respectively at the top, upper middle, lowermiddle, and bottom of the array. As described herein, additional stripesmay also be incorporated, and each stripe may include one or more memorybays. The bit lines within each block are also 2:1 interleaved to relaxthe pitch requirements of the column related circuitry. As an example,bit line 322 is associated with (i.e., driven and sensed by) the uppercolumn circuit block 312, while bit line 324 is associated with thebottom column circuits block 314.

In exemplary embodiments, the memory array 300 is a three-dimensionalmemory array of passive element memory cells formed on each of fourmemory planes. Such memory cells preferably incorporate a trimmableresistor element, as described herein, and may also include an antifuse.Each logical word line is connected to a word line segment on each offour word line layers (each associated with a respective memory plane).

Each stripe of the memory array 300 is divided into a large number ofblocks, such as block 308. In certain exemplary embodiments describedherein, each memory bay includes 16 array blocks, but other numbers ofblocks may be implemented. In the exemplary embodiment depicted, eachblock includes 288 bit lines on each of four bit line layers for therespective four memory planes, thus totaling 1,152 bit lines per block.These bit lines are 2:1 interleaved, so that each of the column decoderand data I/O circuits at the top and bottom of an array block interfacesto 576 bit lines. Other numbers and arrangements of such bit lines andarray blocks, including higher numbers, are also contemplated.

In a selected memory array block, one of these source selection buslines XSELN (or reverse source selection bus XSELP) is decoded anddriven to an active bias condition by a row bias circuit, and remainingbus lines (also called “bias lines”) are driven to an inactive condition(i.e., a voltage suitable for an unselected word line). Consequently, asingle selected RSEL line (i.e., row select line, which corresponds tothe decoded output node 158 in FIG. 3) drives one word line low in theselected memory block, and drives the other N−1 word lines in theselected block to an unselected bias level. In other non-selected memoryblocks, none of the individual bus lines of the source and reversesource selection busses are driven active, so that no word lines areselected by the active RSEL line. Alternatively, the source and reversesource selection busses in unselected array blocks may be left floating,particularly in the forward mode.

Each row select line traverses across all the memory blocks in theentire memory stripe, and drives a respective four-headed word linedriver located “between” each pair of blocks of the stripe (as well astwo more, each respectively located “outside” the first and lastblocks). The RSEL lines may also be known as “global row lines”, and mayalso correspond to the row decoder output nodes referred to herein.Additional details of exemplary circuits, operation, bias conditions,float conditions, modes of operation including read and program modes,and the like, are further described in the aforementioned U.S. Pat. No.6,879,505, and additionally described in U.S. Pat. No. 7,054,219 toChristopher J. Petti, et al., entitled “Transistor Layout Configurationfor Tight-Pitched Memory Array Lines”, the disclosure of which is herebyincorporated by reference in its entirety, and further in U.S.application Ser. No. 11/146,952 filed on Jun. 7, 2005 by Roy E.Scheuerlein, et al., entitled “Decoding Circuit for Non-Binary Groups ofMemory Line Drivers”, the disclosure of which is hereby incorporated byreference in its entirety.

To speed up the selection time of a global row line, these RSEL linesare driven at both ends thereof by two hierarchical row select decoders520, 522 (also known as “global row decoders 520, 522”), eachrespectively located outside the array at left and right sides of thearray stripe. By using a hierarchical decoder structure the size of theglobal row decoder 520 is reduced, thus improving the array efficiency.In addition, a reverse decoding mode may be conveniently provided forimproved testing capability, as further described in “Dual-Mode DecoderCircuit, Integrated Circuit Memory Array Incorporating Same, and RelatedMethods of Operation” by Kenneth K. So, et al., U.S. application Ser.No. 11/026,493 filed Dec. 30, 2004, the disclosure of which is herebyincorporated by reference in its entirety. Exemplary circuits for suchhierarchical decoders may be found in “Apparatus and Method forHierarchical Decoding of Dense Memory Arrays Using Multiple Levels ofMultiple-Headed Decoders,” by Luca G. Fasoli, et al., U.S. PatentApplication Publication No. 2006-0146639 A1, the disclosure of which ishereby incorporated by reference in its entirety.

In certain materials incorporated herein, an exemplary four-headeddecoder circuit includes four “selected” bias lines and a singleunselected bias line. The rationale for such a name is because a givendecoder head couples its output to a “selected” bias line if the inputto the decoder head is selected (i.e., driven to an active level).However, by no means does this imply that all four of the heads showndrive their respective outputs to a level that is reflective of theoutput being selected, because typically only one of the selected biaslines is actually biased in a condition suitable for a selected output,and the remaining three selected bias lines are biased in a conditionsuitable for an unselected output. These “selected” bias for amulti-headed decoder are described herein as a “source selection bus,”but operate similarly, except as noted. Some embodiments also include asecond such bus, being a “reverse source selection bus” rather than asingle unselected bias line.

Conversely, if the input node for the multi-headed decoder is inactiveor unselected, then all such heads drive their respective outputs to anassociated “unselected” bias line (or respective bus line of a reversesource selection bus). For many useful embodiments, such unselected biaslines may be combined into a single bias line shared by all heads of themulti-headed decoder.

Similar or related word line decoder structures and techniques,including additional hierarchical levels of such decoding, bias circuitorganization for the decoded busses (e.g., XSELN and XSELP), and relatedsupporting circuits, are further described in U.S. Pat. No. 6,856,572 byRoy E. Scheuerlein and Matthew P. Crowley, entitled “Multi-HeadedDecoder Structure Utilizing Memory Array Line Driver with Dual PurposeDriver Device”; the disclosure of which is hereby incorporated byreference in its entirety, and in U.S. Pat. No. 6,859,410 by Roy E.Scheuerlein and Matthew P. Crowley, entitled “Tree Decoder StructureParticularly Well-Suited to Interfacing Array Lines Having ExtremelySmall Layout Pitch”, the disclosure of which is hereby incorporated byreference in its entirety.

FIG. 12 is a top view representing a word line layer and a bit linelayer of a three-dimensional memory array in accordance with certainembodiments of the present invention. Other word line layers and bitline layers may be implemented with those shown and would, in someembodiments, share the same vertical connections. Memory blocks 332, 334are shown respectively including a plurality of bit lines 333, 335, andhaving 2:1 interleaved word line segments. Vertical connections to halfof the word line segments for a block are on the left side of the block(e.g., word line segment 337 and vertical connection 339), and verticalconnections to the other half of the word line segments for the blockare on the right side of the block (e.g., word line segment 336 andvertical connection 340). In addition, each vertical connection serves aword line segment in each of two adjacent blocks. For example, verticalconnection 340 connects to word line segment 336 in array block 332 andconnects to word line segment 338 in array block 334. In other words,each vertical connection (such as vertical connection 340) is shared bya word line segment in each of two adjacent blocks. As would beexpected, however, the respective “outside” vertical connections for thefirst and last array blocks may serve only word line segments in thefirst and last array blocks. For example, if block 334 is the last blockof a plurality of blocks forming a memory array (or a memory bay), itsoutside vertical connections (e.g., vertical connection 344) may serveonly the word line segment 342 within block 334, and are thus not sharedby two word line segments as throughout the remainder of the array.

By interleaving the word line segments as shown, the pitch of thevertical connections is twice the pitch of the individual word linesegments themselves. This is particularly advantageous since the wordline pitch which is achievable for many passive element memory cellarrays is significantly smaller than achievable for many via structureswhich might be employed to form the vertical connections. Moreover, thisalso may reduce the complexity of the word line driver circuitry to beimplemented in the semiconductor substrate below the memory array.

Referring now to FIG. 13, a schematic diagram is shown representing athree-dimensional memory array having a segmented word line arrangementin accordance with certain embodiments of the present invention. Eachword line is formed by one or more word line segments on at least one,and advantageously more than one, word line layer of the memory array.For example, a first word line is formed by word line segment 360disposed on one word line layer of the memory array and by word linesegment 362 disposed on another word line layer. The word line segments360, 362 are connected by a vertical connection 358 to form the firstword line. The vertical connection 358 also provides a connection pathto a driver device 356 disposed in another layer (e.g., within thesemiconductor substrate). A decoded output 352 from a row decoder (notshown) traverses substantially parallel to the word line segments 360,362 and, at times, couples the word line segments 360, 362 throughdevice 172 to a decoded bias line 167 (e.g., source selection bus XSELN)which traverses substantially perpendicular to the word line segments,and at other times, couples the word line segments 360, 362 throughdevice 171 to a decoded bias line 203 (e.g., reverse source selectionbus XSELP shown in FIG. 9).

Also shown are word line segments 361, 363 which are connected by avertical connection 359 to form a second word line and to provide aconnection path to the word line driver circuit 175, 176. Anotherdecoded output 353 from the row decoder couples, at times, these wordline segments 361, 363 through device 176 to the decoded source selectline (i.e., “bias line”) 167, and at other times, couples the word linesegments 361, 363 through device 175 to the decoded bias line 203. Whilethis figure conceptually introduces an exemplary array configuration,many embodiments are described herebelow which include variations to theconfiguration shown, and moreover include details which may beappropriate for certain embodiments but not necessarily for allembodiments.

In certain preferred embodiments, a six-headed word line driver isutilized. The six word lines associated with such a six-headed word linedriver circuit are common to two adjacent memory blocks, as described inthe aforementioned U.S. Pat. No. 7,054,219. In other words, a givensix-headed word line driver decodes and drives six word lines in each oftwo adjacent blocks. As implied by the figure, these adjacent blocks maybe viewed as being respectively to the left and to the right of theassociated word line drivers. However, in preferred embodiments suchmulti-headed word line drivers are disposed substantially beneath thearray blocks, and only the vertical connections to the word lines madebetween the blocks.

Certain embodiments are contemplated having non-mirrored arrays (e.g., aword line layer associated with only a single bit line layer), such asis described in U.S. application Ser. No. 11/095,907 filed Mar. 31,2005, by Luca G. Fasoli, et al., entitled “Method and Apparatus forIncorporating Block Redundancy in a Memory Array”, the disclosure ofwhich is hereby incorporated by reference in its entirety. Inparticular, FIG. 15 shows 4 bit line layers, a 16-headed column decoderon both the top and the bottom sides of an array block. This figureshows 4 bit lines on each of 4 bit line layers being coupled by a single16-headed column decoder to the top data bus (describing 4 I/O layers),and likewise 4 bit lines on each of the same 4 bit line layers beingcoupled by a single 16-headed column decoder to the bottom data bus(although in that description, the two groups of 16 selected bit lineswere located within the same array block). Other half-mirroredembodiments are contemplated, such as those sharing a word line layerwith two bit line layers, to form two memory planes.

In the next several figures, various embodiments are described whichutilize reset programming (i.e., reverse bias programming).Consequently, a few definitions are in order for this portion of thedisclosure. The term “set” shall be viewed as forward biasing a single(or group of) memory cells, to cause a lower resistance through eachmemory cell. The term “erase” shall be viewed as forward biasing a blockof memory cells, to cause a lower resistance through each memory cell.Lastly, the term “reset” shall be viewed as reverse biasing a memorycell to cause a higher resistance through each such cell. (With regardto other embodiments described herein such definitions may not apply. Inparticular, the term “erase” may also refer to a reverse bias conditionacross a memory cell to increase the resistance of the cell.)

Referring now to FIG. 14, a memory array 370 includes a first stripe 371and a second stripe 372. The first stripe 371 is also labeled STRIPE 0and the second stripe 372 is also labeled STRIPE 1. Stripe 371 includestwo memory bays, BAY_00 and BAY_01. Each such memory bay includes aplurality of array blocks (e.g., 16 such memory array blocks). Whilethis exemplary memory array 370 is shown including two memory stripes,each having two memory bays, other numbers of stripes and bays are alsocontemplated.

The first memory bay, BAY_00 is representative of the other memory bays.A total of 16 memory array blocks are represented, two of which arelabeled as 374 and 375, each having a sense amplifier disposed below thememory array (e.g., in the semiconductor substrate layers, whereas oneor more memory planes may be formed above a dielectric layer formed onthe substrate layers). A top column decoder circuit 380, a top data bus373, and a top bit line select block 381 span across the 16 array blocksof this bay, and are associated with those bit lines exiting the topside of each array block. A bottom column decoder circuit 379, a bottomdata bus 378, and a bottom bit line select block 382 span across the 16array blocks of this bay, and are associated with those bit linesexiting the bottom side of each array block.

It should be understood that the top column decoder circuit 380 may bedescribed as being “above” the array blocks, while the bottom columndecoder circuit 379 may be described as being “below” the array blocks.This terminology reflects visually the orientation of the circuit blocksas depicted in the schematic diagrams. Such locations may also bedescribed as “to one side” and “to the opposite side” of the arrayblocks (although admittedly this implies a horizontal substrate for theintegrated circuit upon which this circuit is implemented). In addition,the directional terms “north” and “south” are convenient terms fordescribing the positional relationships of various circuit blocks.

In contrast, in certain embodiments the memory array may be formed“above” the substrate, and various circuit blocks being described asbeing “below” the memory array. As used herein, being “above” or “below”the substrate or a memory array block, which are actual physicalstructures having generally a planar character, is relative to adirection normal to the surface of such a substrate or memory plane.

In FIG. 14, although the bottom column decoder may be described as being“below” the array blocks, such a column decoder is not necessarilybeneath the memory array (i.e., closer to the substrate). In contrast,the sense amplifier blocks labeled SA which are depicted as within thearray block boundary, and are described as being “below” or “beneath”the array block, may be assumed to convey such a physical location andstructural relationship. In the context of the description and variousfigures, the usage of “above” and “below” should be clear.

In certain exemplary embodiments, the bit line decoders are 16-headeddecoders, and simultaneously select 16 bit lines on the top side of aselected memory array block. This “selection” is in regards to thecolumn decoding, and does not necessarily imply that all 16 bit linesare actually programmed at the same time. The sixteen selected bit linesare preferably arranged as four adjacent bit lines which exit the arrayat the top (or the bottom for the other decoder), on each of four bitline layers.

The sixteen I/O lines of the top data bus 373 traverse horizontallyacross all sixteen blocks. Such a bus corresponds to the SELB busdescribed above. Each of the individual bus lines of this data bus 373is coupled to a respective one of sixteen sense amplifier circuits whichare distributed among the sixteen blocks as shown. Each of the sixteendata bus lines may also be coupled to an associated bias circuit (i.e.,a reset circuit), which may be used during a particular mode ofoperation to properly bias the respective bit lines within the“selected” 16 bit lines. For example, for a reset programming mode ofoperation, such a reset circuit properly biases those bit lines to beprogrammed and those bit lines not to be programmed within the“selected” 16 bit lines, in accordance with the data bit for each of the16 bit lines, and also in accordance with the number of bit lines whichare allowed to be simultaneously programmed (meaning, of course, thecell to be programmed which is coupled to the particular bit line).These bias circuits may be disabled and caused to exhibit a high outputimpedance during a read mode of operation when the selected bit linesare coupled to respective sense amplifiers by way of the data bus 373(i.e., the SELB bus described above).

The sixteen I/O lines of the bottom data bus 378 traverse horizontallyacross all sixteen blocks. Such a bus corresponds to another SELB busdescribed above, this time for the bit lines exiting at the bottom ofthe array (remembering that the bit lines are 2:1 interleaved). Asbefore, each of the individual bus lines of this data bus 378 is coupledto a respective one of sixteen sense amplifier circuits which aredistributed among the sixteen blocks as shown. In every group of 16blocks (i.e., a bay) there are 32 sense amplifiers which connect to 32selected bit lines. In the read mode, all the select bit lines may bearranged to fall within one of the sixteen blocks, or may be arrangedotherwise, as will be discussed here. The sense amplifiers may beconveniently implemented beneath the memory array block, whereas thedata bus lines 373, 378, the sixteen-headed column select decoders(i.e., the bit line select blocks 381, 382), and a small portion of thecolumn decoders 380 are preferably implemented outside the array block.Additional details of useful column decoder arrangements may be found inthe aforementioned U.S. application Ser. No. 11/095,907, and in theaforementioned U.S. Patent Application Publication No. 2006-0146639 A1.

In a programming mode, the magnitude of the total programming currentmay limit the number of simultaneously programmed memory cells. Inaddition, the magnitude of the programming current which flows along asingle selected bit line or word line may also limit the number ofmemory cells which may reliably be programmed at the same time. In theexemplary architecture shown, if both column decoders select bit linesin the same array block, there would be 32 total bit lines selected withone array block. Assuming each decoder selects four bit lines from eachof four bit line layers (i.e., four bit lines from each respectivememory plane), then the selected word line segment on each memory planewould have to support the programming current for a total of eightselected memory cells. (See FIG. 13 to show individual word linesegments per layer.) Four of these selected memory cells are associatedwith bit lines exiting to the north, and the other four selected memorycells are associated with bit lines exiting to the south. All 32 of theselected memory cells would be driven by the same word line drivercircuit, whereas each of the selected memory cells is driven by its ownbit line driver circuit.

As implied above, even if the total programming current for 32 cellscould be supplied by the integrated circuit, the programming current for8 selected memory cells may cause an unacceptable voltage drop along theselected word line segments on each layer. In addition, the selectedword line driver circuit may not be capable of driving such current withacceptable voltage drop.

In a reset programming mode, a reverse bias is applied to each selectedpassive element cell, whereby the modifiable resistance material isreset to a high resistance state to program user data. One or more bitlines in a block may be selected for simultaneous programming, and assome of the bits reset to a higher resistance state, the current flowingfrom the selected bit line to the selected word line decreasessignificantly, and the remaining bits see a slightly higher voltage dueto decreasing word line IR drops. As a result, the bits that programmore easily change state first, which allows the more “stubborn” bits tosee a slightly higher voltage to help program such bits.

Nonetheless, having all 32 selected memory cells reside in the samearray block may be unacceptable for either of the reasons stated above.Consequently, two different array blocks may be selected forprogramming, each using a respective one of the two data busses. In thefigure, the array block 374 is cross-hatched to signify its selectionfor reset programming. One of the top column decoder 380 outputs forblock 374 is active, thus coupling 16 selected bit lines to the top databus 373 (signified by the arrowhead from the array block 374 to the databus 373). In addition, the array block 375 is cross-hatched to signifyits selection for reset programming. One of the bottom column decoder379 outputs for block 375 is also active, thus coupling 16 selected bitlines to the bottom data bus 378 (signified by the arrowhead from thearray block 375 to the data bus 378).

A single row 377 is selected by the global row decoders on either sideof the memory array (not shown), which drives a global row select lineacross the entire stripe 371. Such a global row select line correspondsto the decoded output 158 of the row decoder circuit shown in FIG. 9. Amulti-headed word line driver circuit is enabled (by appropriate biasconditions on its source selection bus and reverse source selection bus)to drive a selected word line 376 in block 374, and a selected word linein block 375. Since the word lines in this exemplary embodiment areshared, one such selected word line driver circuit drives the word linein both blocks 374, 375. The entire programming current is still sourcedthrough this one selected word line driver circuit, but now the currentalong each selected word line segment is reduced in half, as each wordline segment now supports only 4 selected memory cells. Note the nexthigher or lower word line in blocks 374 and 375 are driven by twoseparate word line driver devices and the peak current in either of thewordline driver devices would be about half. By choosing to arrange thepages of data in a more complex arrangement of blocks corresponding toodd or even word lines, shared word line drivers can be avoidedentirely. For example, assume that even word lines are driven from theleft side of a given array block, and that odd word lines are drivenfrom the right side of a given array block. When an even word line isselected in the given array block, the block to its left may besimultaneously selected, and when an odd word line is selected in thegiven array block, the block to its right may be simultaneouslyselected. In such a case, no selected word lines appear in an unselectedarray block. In an alternate embodiment, the page of data to be writtenmay be arranged to avoid shared word line drivers.

In the above dual data bus example, each memory block is associated withboth data busses 373, 378. In a different memory cycle, other bit linesassociated with array block 374 would be coupled to the bottom data bus378, and other bit lines associated with array block 375 would becoupled to the top data bus 373. In this and other embodiments, tooptimize performance the blocks selected for read in a given bay aredifferent than the blocks selected for reset. A single block is selectedat a time for read, but two blocks are selected for reset. The two databusses are both active for read but access a single block, unlike thereset access described above.

There are a variety of other dual data bus arrangements that providesimilar benefit. FIG. 15 shows a memory bay 400 in which the odd memoryblocks are associated with only a first data bus, and the even memoryblocks are associated with only a second data bus. Odd array block 406is associated with the first data bus 402, which is represented by thebit line select block 408, and even array block 407 is associated withthe second data bus 404. Two memory array blocks (e.g., array blocks406, 407) are simultaneously selected, each coupling its selected bitlines to one of the data busses (represented by respective bold arrows410, 412).

FIG. 16 shows a memory bay 420 in which each memory block is associatedwith both a first data bus 422 and a second data bus 424. In onedepicted memory cycle, the first array block 426 is selected and couples(bold arrow 430) its selected bit lines to the first data bus 422, whilethe second array block 427 is simultaneously selected and couples (boldarrow 432) its selected bit lines to the second data bus 424. In anothermemory cycle, the first array block 426 could be selected and couplesits selected bit lines to the second data bus 424, while the secondarray block 427 is simultaneously selected and couples its selected bitlines to the first data bus 422.

FIG. 17 shows a memory bay 440 in which each memory block is associatedwith both a first data bus 442 and a second data bus 444, which are bothlocated on the same side of the array blocks. The first array block 446is associated with the first data bus 442 by virtue of a first bit lineselect block 449, and is also associated with the second data bus 444 byvirtue of a second bit line select block 448. In the exemplary memorycycle shown, two memory array blocks (e.g., array blocks 446, 447) aresimultaneously selected, each respectively coupling its selected bitlines to the first and second data busses 442, 444 (represented byrespective bold arrows 450, 454).

Referring now to FIG. 18, a memory bay 460 is depicted which is similarto the memory bay BAY_00 shown above, except in this exemplaryembodiment, two simultaneously selected array blocks 462, 464 arenon-adjacent. In one depicted memory cycle, array block 462 is selectedand couples (i.e., the bold arrow) its selected bit lines to an upperdata bus 466, while array block 464 is simultaneously selected andcouples its selected bit lines to a lower data bus 468. Thisorganization is particularly useful if the word lines are not sharedbetween adjacent memory aray blocks, but can be used even if such wordlines are shared. In such a case, a selected word line in a selectedblock will also hang over into the adjacent memory block.

In each of these illustrated embodiments, more than one block isselected for reset programming. Reverse bias is applied to the passiveelement cells in the selected array blocks (i.e., selected “sub arrays”)whereby the modifiable resistance material is reset to a high resistancestate to program user data into the array. This may be accomplished athigh bandwidth for at least several reasons. First, by selecting morethan one block for programming, the number of simultaneously programmedmemory cells can be increased beyond the limits imposed by a given wordline segment, or even by a given word line driver circuit. More than twoselected array blocks could be selected, as long the data busses reacheach such block. In addition, the direction of programming assists inallowing a greater number of cells to be programmed. In other words, assome of the programmed bits reset to a higher resistance state, themagnitude of the current flowing from the bit line to the word linedrops significantly, and the remaining bits see slightly higher voltagedue to decreasing word line IR drops. For a given maximum programmingcurrent, it is likely possible to reliably program more bits from low tohigh resistance than from high to low resistance. Also contributing to ahigh bandwidth programming is the bias conditions on all the largenumber of unselected word lines and bit lines. Since these all remain atground, there are not large delays associated with biasing up theunselected array lines as array blocks are selected and deselected, norare there large current transient currents that must be accommodated tobias up and down such array blocks. Of note, in this reset programmingarrangement, even the unselected word lines and bit lines in theselected memory block are biased at ground (i.e., left floating whenusing certain exemplary decoder structures).

In exemplary embodiments, a memory chip may be organized so that eachbay has its own set of read write circuits and at least one data busconnecting the read/write circuits to the bit line select circuitry.This bus extends across the width of the bay, or in other words “spans”the group of blocks. There may be a column decoder at the top side ofthe blocks and a second column decoder at the bottom side of the blocksso that there are two data busses. In certain embodiments, there may betwo sets of read write circuits associated with each respective databus. Preferably a particular page of data is spread to all the bays forhighest bandwidth. This is depicted in the exemplary embodiment shown inFIG. 14 by a pair of selected array blocks within each memory bay.

Preferably the selected bits are distributed over two blocks in a bay,one block having bit lines selected by one of the column decoders andassociated with one of the data busses, and the second block selected bythe other column decoder and data bus so that the bandwidth is doubledper bay, but the current flowing in any one word line segment isunchanged. In addition, one or many of the bit lines at a selectedcolumn location are selected for reset programming simultaneously. Thenumber simultaneously programmed may be limited by the current flowingfrom the selected bits lines in a block to the common word line. Butthis limitation is mitigated in a method where, as some of the bitsreset to a higher resistance state, the current through the “alreadyreset” cell decreases, the IR drop along the common word line segmentdecreases, and remaining bits get more voltage to encourage their reset.

The selected word lines in each selected block are preferably all on thesame row, which eases decoding implications because the global rowdecoder circuit needs no change to support this. Preferably thesimultaneously selected blocks are adjacent, particularly if word linesare shared between adjacent blocks. The decoding may be arranged sothat, for any selected word line shared between two adjacent blocks,these two adjacent array blocks may be configured to be thesimultaneously selected array blocks. For example, a given word linedriver disposed between the first and second blocks drives a shared wordline in the first and second blocks, which are both selected. The nextword line (assuming they are 2:1 interleaved form left and right sidesof the array blocks) would be driven from an array line driver betweenthe second and third array blocks, which could also be the selectedarray blocks. This avoids dealing with selected word lines hanging overinto adjacent non-selected array blocks.

When using reset programming, each memory cell is set back to a lowresistance state by the “set” mode of operation, which may be used torewrite new data, or erase a group of bits, by applying forward bias toone bit at a time, or many bits in a page of data or an erase block.High performance erase may be achieved by selecting multiple bit linesand or multiple word lines in a block, and setting the cells to lowresistance. Current limiting circuitry in the bit line driver pathlimits the total current flowing to the common word line. Depending uponthe memory cell technology chosen, and the relative magnitude of the setcurrent and reset current, and the magnitude of U cell leakage current,fewer blocks may be selected for the set or erase operation than forreset (i.e., programming).

One choice of resistive material is the polysilicon material that formsthe diode. An antifuse (“AF”) can be in series with the polysilicondiode, and the antifuse is popped before the programming event in aformatting step in manufacturing. The antifuse serves to limit themaximum current that the cell will conduct when set.

As stated above, preferably the memory array includes a segmented wordline architecture (as depicted in FIGS. 12 and 13), and preferably a 3Darray. In certain embodiments, the word lines on a given word line layerare associated with bit lines on a single bit line layer, while incertain embodiments the word lines on a given word line layer are sharedbetween two bit line layers (i.e., a single word line layer and two bitline layers defining two memory planes) in a so-called “half-mirrored”arrangement. Such a memory array structure is described further in theaforementioned U.S. Pat. No. 6,879,505.

The description of the various decoder circuits thus far has largelyfocused on describing a single array block. Recall that each decoder hasbeen described in the context of a source selection bus and, for some ofthe embodiments, a reverse source selection bus. The word line decoderhierarchy may be viewed as relatively straightforward. The sourceselection bus and unselected bias line, or alternatively the reversesource selection bus, are decoded based upon address information, anddriven according to which array block is active. Similar row decodercircuits are referred to already elsewhere herein. The respective sourceselection bus(ses) and/or unselected bias lines for word linesassociated with unselected array blocks may be left floating.

As for the column decoder arrangements, a hierarchical bus arrangementmay be employed to provide efficient routing of read/write data, andefficient biasing of bit lines within selected and unselected arrayblocks. Useful hierarchical bus arrangements will be described in thecontext of the dual source selection bus decoders depicted in FIGS. 9and 10, although these may be adapted for the other decoder embodiments.

In the forward operations (read and set) an exemplary hierarchical busarrangement provides a suitable bias on the SELN bus for a selectedarray block, and leaves the SELN bus for unselected array blocksfloating. This is helpful to reduce unwanted power dissipation in thearray blocks adjacent to a selected array block. The unselected wordlines in a selected array block are biased at a fairly high voltage VUX(e.g., VPP−VT), and with a shared word line architecture theseunselected word lines also extend to the adjacent non-selected arrayblock (i.e., half of the word lines within the non-selected array blockbeing shared with the selected array block). The unselected bit lines inthe adjacent array block preferably are biased at the unselected bitline voltage, VUB (e.g., VT). This wastes power due to the leakagecurrents through unselected memory cells. The other half of the wordlines in the adjacent non-selected array block are floating, so thatthey leak up to the VUB voltage, and leakage power is minimized for halfof the unselected cells.

The exemplary hierarchical bus arrangement also provides, in a resetmode of operation, a long SELN path spanning many blocks to reach thereset data drivers distributed under the array blocks.

Four exemplary hierarchical bus arrangements are depicted in the nextfour figures. Referring now to FIG. 19, a bus arrangement 500 isdepicted and includes three memory array blocks 502, 504, 506, whichrepresent all the array blocks in a bay. While only three array blocksare shown, the incremental nature of the arrangement will be clear, aswill its extendibility to any number of array blocks. A respective SELNbus segment is shown for each respective array block. As used herein, abus segment is merely a smaller bus than other such busses, and in otherembodiments (described below), multiple bus segments may be coupledtogether to form single larger bus.

In the set mode, the SELN bus segment for a selected array block iscoupled to a longer GSELN bus which spans the entire memory bay by acoupling circuit 508. This coupling circuit 508 may be as simple as 16transistors, each coupling a respective SELN bus line to the respectiveGSELN bus line. This coupling circuit 508 is enabled by a control signalEN_GSELN, which is active for the selected array block when in the setmode, or in the reset mode (discussed below). During the set mode, thisGSELN bus is coupled to the unselected bit line voltage VUB (i.e., eachbus line of the GSELN bus is coupled to this voltage). The respectiveEN_GSELN control signal for the unselected array blocks is inactive, therespective coupling circuit 508 turned off, and thus the respective SELNbus segment left floating, as desired.

In the reset mode, the respective EN_GSELN control signal for all arrayblocks is active, and the respective coupling circuit 508 is turned onto couple the respective SELN bus segment to the GSELN bus. Thisprovides the write data to all array blocks, irrespective of which isselected. The SELB bus is driven to the VUX voltage (e.g., ground) toprovide the unselected bit line bias condition for reset programming.

This is a relatively simple circuit arrangement that only requires anadditional 16 global lines (GSELN) and 16 extra transistors per arrayblock (the coupling circuit 508). Disadvantages (at least relative toother embodiments described below) include a relatively high capacitanceon both the SELB and SELN busses. The capacitance on the SELB bus existsat all times, but is detrimental only during a read cycle, whereas thehigh capacitance on the SELN bus exists during the reset mode when allthe SELN bus segments are coupled to the global bus GSELN, during whichtime the combined busses convey the reset data information.

In certain other embodiments, the reset mode may be configured withentirely non-negative voltages, rather than splitting the reset voltageVRR into −VRR/2 and +VRR/2. In such cases, the unselected word lines andbit lines are biased at the midpoint, which is now VRR/2. Consequently,when coming out of reset mode, care should be exercised to control therate of discharge of these lines to avoid excessive current surges whendischarging.

Referring now to FIG. 20, another embodiment is depicted in which therespective SELN bus segments are coupled together to form a singlelarger bus which spans the entire memory bay. In the set mode, the SELNbus segment for a selected array block is coupled to a single bias lineVUB which spans the entire memory bay by a coupling circuit 532. Thiscoupling circuit 532 may be as simple as 16 transistors, each coupling arespective SELN bus line to the VUB bias line (which is coupled to anappropriate bias circuit, as indicated). This coupling circuit 532 isenabled by a control signal BLATVUB, which is active for the selectedarray block when in the set mode. For the unselected array blocks, therespective BLATVUB control signal is inactive, the respective couplingcircuit 532 turned off, and thus the respective SELN bus segment leftfloating, as desired.

In the reset mode, the SELB bus is driven to the VUX voltage (e.g.,ground) to provide the unselected bit line bias condition for resetprogramming. In addition, the respective SELN bus segments are coupledtogether by a coupling circuit 533 to form a single bus which spans theentire memory bay, which is coupled to the reset circuit to provide tothe combined busses the reset data information. One of the SELN bussegments may be coupled to the reset circuit by bus 536. In certainembodiments, a coupling circuit 535 may be utilized to provide theconnection to the reset block in the RESET mode.

This is a relatively simple circuit arrangement that only requires oneadditional bias line (VUB) and 32 extra transistors per array block (thecoupling circuits 532, 533). Like the previous embodiment, there isstill a relatively high capacitance on both the SELB and SELN busses.

Referring now to FIG. 21, a bus arrangement 550 is depicted whichincorporates feature from both previous embodiments. In the SET mode,the SELN bus segment for a selected array block is coupled to a VUB biasline which spans the entire memory bay by a coupling circuit 554, whichis enabled by a control signal BLATVUB. The respective BLATVUB controlsignal for the unselected array blocks is inactive, the respectivecoupling circuit 554 turned off, and thus the respective SELN bussegment left floating, as desired (since the EN_GSELN signal is alsoinactive in the SET mode).

In the reset mode, the respective EN_GSELN control signal for a selectedarray block is active, and a respective coupling circuit 552 is turnedon to couple the respective SELN bus segment to the GSELN bus. Therespective EN_GSELN control signal for the unselected array blocks isinactive, the respective coupling circuit 552 turned off, and therespective SELN bus segment left floating. This configuration providesthe write data to only the selected array block(s), which reduces thetotal capacitance significantly. The SELB bus is driven to the VUXvoltage (e.g., ground) to provide the unselected bit line bias conditionfor reset programming.

This circuit arrangement requires 17 additional lines (VUB bus and GSELNbus) and 32 extra transistors per array block (the coupling circuits552, 554). Unlike the previous embodiments, this arrangement providesfor significantly reduced capacitance on the SELN bus, since therespective SELN bus segments for unselected array blocks are not coupledto the GSELN bus. There remains fairly high capacitance on the SELB bus.

FIG. 22 depicts yet another hierarchical bus arrangement, this timeutilizing only a single global select bus GSEL spanning the memory bay,and divides the SELB bus into a respective SELB bus segment for eacharray block. For a selected array block, either the respective SELB busor the respective SELN bus segment is coupled to this GSEL bus. DuringSET mode, the selected block SELB bus segment is coupled to the GSELbus, and the selected block SELN bus segment is coupled to the VDSELbias line (which during SET conveys the unselected bit line biascondition, VUB, generated by an appropriate bias circuit, as indicated).The unselected block SELN busses are left floating.

During RESET mode, the selected block SELN bus segment is coupled to theGSEL bus, and the selected block SELB bus segment is coupled to theVDSEL bias line (which during RESET conveys the unselected word linebias condition, VUX). The unselected block SELN busses are again leftfloating.

This arrangement is the most complex of those described, requiring 17global lines (i.e., spanning the memory bay) and 64 extra transistorsper array block, and may require more layout area in some embodiments.However, it also provide low capacitance on the SELB and SELN busses,and thus would allow higher performance, and provides a very modularblock design. Moreover, larger memory bays may be implemented withoutsignificantly increasing the capacitance on the SELB and SELN busses.

In another embodiment, the column decoder circuits could be modified toprovide a separate column decode outputs for the NMOS and PMOStransistors of the bit line driver circuit so the bit line selector canbe put in high impedance state. But this arrangement would significantlyincrease the area of the bit line selector, as well as the columndecoder itself.

Referring now to FIG. 23, a data circuit is depicted which includesseparate blocks for the set, reset, and read modes. Recall that, in thereverse bias mode (i.e., reset mode), the selected bit lines are coupledto a respective SELN bus line (i.e., the reverse source selection bus).Here we find a reset driver 615 coupled to the SELN bus 617 (whichrepresents the path to the SELN bus for any of the four hierarchical busarrangements which may be employed. In essence, this represents the pathwhich ultimately is coupled to the SELN bus segment for a selected arrayblock. Data information to be written is received into I/O logic 601,conveyed on bus 602 to a write latch block 604, conveyed on bus 607 tocontrol logic 608, which then controls the reset driver 615 by way ofcontrol lines 612.

Recall that, in the forward mode, the selected bit lines are coupled toa respective SELB bus line. Since both the SET and READ modes utilizethe forward bias mode, both a set driver 614 and a read sense amplifier613 are coupled to the SELB bus 616 (which represents the path to theSELB bus for any of the four hierarchical bus arrangements above, or anyother arrangement which may be employed). Sensed data is conveyed by bus609 to a read latch 605, with is conveyed by bus 603 to the I/O logic601. The various busses 606, 610, and 611 provide for a programmingcontrol loop, sometimes called smart write, which can shut off theprogramming current when a bit is successfully popped or set. The bussesalso provide for a read before write capability to determine, forexample, any previously-programmed state (e.g., LSB data bit) thatshould be preserved during a subsequent programming operation. Such acapability is described further in the 023-0049 and 023-0055applications, referenced below.

A simplified exemplary reset driver 615 is depicted in FIG. 24, alongwith a representation of the word line and bit line selection paths to aselected memory cell 638. A word line selection path 639 represents thepath through the word line driver circuit (i.e., the decoder head) andto the circuit for generating the decoded source selection bus XSELN. Abit line selection path 636 represents the path through the bit linedriver circuit and through any bus coupling circuits, such as thosedescribed in the various hierarchical bus arrangement embodiments, tothe individual SELN bus line 635. A preferred reset method andassociated reset driver is described in the SAND-01114US0 andSAND-01114US1 applications referenced below, particularly in regards toFIG. 13 therein.

The capacitance of the bit line selection path are precharged beforeattempting to program a newly addressed selected bit line. This may beperformed using a higher magnitude of current than is desirable toactually reset the selected memory cell, but if timed properly, such ahigher magnitude precharge can speed up the precharge time withoutdetrimental effect to the memory cell. This precharge is controlled by aprecharge column signal PCHGCOL conveyed on control signal 637 to thebit line selection path 636. A bit line precharge (BLP) current limitcircuit 633 and a reset limit circuit 634 are both provided to controlthe upper magnitude of the respective bit line precharge and resetcurrents. Both are disabled by signal 632 if the data is such that noreset operation is necessary, and the SELN bus line 635 floats.

Conversely, if the data in is such that the memory cell is to be reset,the disable line 632 is inactive, and the BLP current limit circuit 633is enabled briefly (e.g., 200-500 ns) to provide a higher level ofcontrolled current for such precharge, after which it is disabled (by acontrol signal not shown), leaving the reset current limit circuit 634to supply a lower magnitude of current for resetting the selected memorycell. Since resetting a memory cell causes it to change from a lower toa higher resistance state, there is little need to sense completion ofthe reset operation and disable the reset limit 634, since the cellturns off by itself as soon as it reaches the reset state.

As regards various embodiments described above, many types of memorycells are capable of being programmed using a reverse bias (e.g., thereset mode described above). Such cells include a passive element cellhaving a metal oxide (e.g., a transition metal oxide) and a diode. Othersuitable cells include those having a resistive material in a diodematrix. Examples include a programmable metallization connection, aphase change resistor such as GST material, an organic material variableresistor, a complex metal oxide, a carbon polymer film, a dopedchalcogenide glass, and a Schottky barrier diode containing mobile atomsto change resistance. The resistive material chosen may provideone-time-programmable (OTP) memory cells, or write-many memory cells. Inaddition, a polysilicon diode could be employed having conductionmodified by reverse bias stress.

Useful memory cells for reverse reset operation are described in U.S.Pat. No. 6,952,030 entitled “High-Density Three-Dimensional Memory Cell”to S. Brad Herner, et al.; and also in U.S. application Ser. No.11/237,167 entitled “Method for Using a Memory Cell ComprisingSwitchable Semiconductor Memory Element with Trimmable Resistance” byTanmay Kumar, et al., filed on Sep. 28, 2005. A suitable metal oxidememory cell is shown in U.S. application Ser. No. 11/394,903 filed onMar. 31, 2006, entitled “Multilevel Nonvolatile Memory Cell Comprising aResistivity-Switching Oxide or Nitride and an Antifuse” by S. BradHerner. A suitable memory cell using a phase change material, which canprovide multiple resistance states, is shown in U.S. Patent ApplicationPublication No. 2005-0158950 entitled “Non-Volatile Memory CellComprising a Dielectric Layer and a Phase Change Material in Series” byRoy E. Scheuerlein, et al. Each of these above-referenced disclosures isincorporated herein by reference in its entirety. Other exemplary memorycells having a transition-metal oxide (e.g., including those havingcobalt), and exemplary cells in which the polysilicon material of thesteering element itself comprises the switchable resistance material,are described in the MA-163-1 application referenced below.

In addition, U.S. application Ser. No. 11/125,939 filed on May 9, 2005,entitled “Rewritable Memory Cell Comprising a Diode and a ResistanceSwitching Material” by S. Brad Herner, et al., discloses a usefulrewritable memory cell incorporating a diode in series with an oxide,such as a nickel oxide, in which the resistance of the memory cell maybe repeatedly switched from low to high and from high to low resistancestates. U.S. application Ser. No. 11/395,995 filed on Mar. 31, 2006,entitled “Nonvolatile Memory Cell Comprising a Diode and a ResistanceSwitching Material” by S. Brad Herner, et al., discloses a OTPmulti-level memory cell which is set using forward bias and reset usingreverse bias. Each of these above-referenced disclosures is incorporatedherein by reference in its entirety.

In many of the embodiments described herein, the precise bias conditionsimposed upon each respective bus line in the data path is independentlycontrollable. The specific voltage and current settings for each of theset and reset drivers can be adjusted for each bit of the data path. Asa result, certain memory cells having more than two states (i.e.,“multi-level” memory cells) are contemplated for use with many of thestructures described herein. Exemplary multi-level memory cells aredescribed in U.S. application Ser. No. 11/237,167 filed on Sep. 28, 2005entitled “Method for Using a Memory Cell Comprising SwitchableSemiconductor Memory Element with Trimmable Resistance” by Tanmay Kumar,et al., the disclosure of which is incorporated herein by reference inits entirety, and in the MA-163-1 application, referenced below.

Exemplary passive element memory cells and related non-volatile memorystructures which may be useful in practicing the present invention aredescribed the following documents, each of which is incorporated hereinby reference in its entirety:

-   -   U.S. Pat. No. 6,034,882 entitled “Vertically Stacked Field        Programmable Nonvolatile Memory and Method of Fabrication” to        Mark G. Johnson, et al.;    -   U.S. Pat. No. 6,420,215 entitled “Three Dimensional Memory Array        and Method of Fabrication” to N. Johan Knall, et al.;    -   U.S. Pat. No. 6,525,953 entitled “Vertically-Stacked, Field        Programmable, Nonvolatile Memory and Method of Fabrication” to        Mark Johnson, et al.;    -   U.S. Pat. No. 6,490,218 entitled “Digital Memory Method and        System for Storing Multiple-Bit Digital Data” to Michael Vyvoda,        et al.;    -   U.S. Pat. No. 6,952,043 entitled “Electrically Isolated Pillars        in Active Devices” to Michael Vyvoda, et al.; and    -   U.S. Patent Application Publication No. US2005-0052915 entitled        “Nonvolatile Memory Cell Without a Dielectric Antifuse Having        High- and Low-Impedance States” by S. Brad Herner, et al.

The following applications, each filed on even date herewith, describememory cell structures, circuits, systems, and methods that may beuseful in practicing the present invention, each of which isincorporated herein by reference in its entirety:

-   -   U.S. application Ser. No. ______ (Attorney Docket No. 10519-141)        entitled “Multi-Use Memory Cell and Memory Array” by Roy        Scheuerlein and Tanmay Kumar (the “10519-141” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 10519-150)        entitled “Method for Using a Multi-Use Memory Cell and Memory        Array” by Roy Scheuerlein and Tanmay Kumar (the “10519-150”        application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 10519-142)        entitled “Mixed-Use Memory Array” by Roy Scheuerlein (the        “10519-142” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 10519-151)        entitled “Method for Using a Mixed-Use Memory Array” by Roy        Scheuerlein (the “10519-151” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 10519-149)        entitled “Mixed-Use Memory Array With Different Data States” by        Roy Scheuerlein and Christopher Petti (the “10519-149”        application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 10519-152)        entitled “Method for Using a Mixed-Use Memory Array With        Different Data States” by Roy Scheuerlein and Christopher Petti        (the “10519-152” application);    -   U.S. application Ser. No. ______ (Attorney Docket No.        SAND-01114US0) entitled “Controlled Pulse Operations in        Non-Volatile Memory” by Roy Scheuerlein (the “SAND-01114US0”        application);    -   U.S. application Ser. No. ______ (Attorney Docket No.        SAND-01114US1) entitled “Systems for Controlled Pulse Operations        in Non-Volatile Memory” by Roy Scheuerlein (the “SAND-01114US1”        application);    -   U.S. application Ser. No. ______ (Attorney Docket No.        SAND-01115US0) entitled “High Bandwidth One-Time        Field-Programmable Memory” by Roy Scheuerlein and Christopher J.        Petti (the “SAND-01115US0” application);    -   U.S. application Ser. No. ______ (Attorney Docket No.        SAND-0115US1) entitled “Systems for High Bandwidth One-Time        Field-Programmable Memory” by Roy Scheuerlein and Christopher J.        Petti (the “SAND-01115US1” application);    -   U.S. application Ser. No. ______ (Attorney Docket No.        SAND-01117US0) entitled “Reverse Bias Trim Operations in        Non-Volatile Memory” by Roy Scheuerlein and Tanmay Kumar (the        “SAND-01117US0” application);    -   U.S. application Ser. No. ______ (Attorney Docket No.        SAND-01117US1) entitled “Systems for Reverse Bias Trim        Operations in Non-Volatile Memory” by Roy Scheuerlein and Tanmay        Kumar (the “SAND-01117US1” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. MA-163-1)        entitled “Method for Using a Memory Cell Comprising Switchable        Semiconductor Memory Element with Trimmable Resistance” by        Tanmay Kumar, S. Brad Herner, Roy E. Scheuerlein, and        Christopher J. Petti (the “MA-163-1” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 023-0048)        entitled “Passive Element Memory Array Incorporating Reversible        Polarity Word Line and Bit Line Decoders” by Luca G. Fasoli,        Christopher J. Petti, and Roy E. Scheuerlein (the “023-0048”        application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 023-0054)        entitled “Method for Using a Passive Element Memory Array        Incorporating Reversible Polarity Word Line and Bit Line        Decoders” by Luca G. Fasoli, Christopher J. Petti, and Roy E.        Scheuerlein (the “023-0054” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 023-0049)        entitled “Apparatus for Reading a Multi-Level Passive Element        Memory Cell Array” by Roy E. Scheuerlein, Tyler Thorp, and        Luca G. Fasoli (the “023-0049” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 023-0055)        entitled “Method for Reading a Multi-Level Passive Element        Memory Cell Array” by Roy E. Scheuerlein, Tyler Thorp, and        Luca G. Fasoli (the “023-0055” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 023-0051)        entitled “Dual Data-Dependent Busses for Coupling Read/Write        Circuits to a Memory Array” by Roy E. Scheuerlein and Luca G.        Fasoli (the “023-0051” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 023-0056)        entitled “Method for Using Dual Data-Dependent Busses for        Coupling Read/Write Circuits to a Memory Array” by Roy E.        Scheuerlein and Luca G. Fasoli (the “023-0056” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 023-0052)        entitled “Memory Array Incorporating Two Data Busses for Memory        Array Block Selection” by Roy E. Scheuerlein, Luca G. Fasoli,        and Christopher J. Petti (the “023-0052” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 023-0057)        entitled “Method for Using Two Data Busses for Memory Array        Block Selection” by Roy E. Scheuerlein, Luca G. Fasoli, and        Christopher J. Petti (the “023-0057” application);    -   U.S. application Ser. No. ______ (Attorney Docket No. 023-0053)        entitled “Hierarchical Bit Line Bias Bus for Block Selectable        Memory Array” by Roy E. Scheuerlein and Luca G. Fasoli (the        “023-0053” application); and    -   U.S. application Ser. No. ______ (Attorney Docket No. 023-0058)        entitled “Method for Using a Hierarchical Bit Line Bias Bus for        Block Selectable Memory Array” by Roy E. Scheuerlein and Luca G.        Fasoli (the “023-0058” application).

As should be appreciated, specific exemplary embodiments shown hereinhave been described in the context of specific numeric examples, such asthe number of decoded outputs, the number of decoder heads, the numberof bus lines, the number of data busses, the number of array blockswithin a memory bay, and the number of memory stripes. Other variationsconsistent with other design objectives may be implemented using theteachings of this disclosure. In the interest of clarity, not all of theroutine features of the implementations described herein are shown anddescribed.

Most memory arrays are designed having a relatively high degree ofuniformity. For example, usually every bit line includes the same numberof memory cells. As another example, the number of bit lines, wordlines, array blocks, and even memory planes is frequently an integralpower of two in number (i.e., 2^(N)), for ease and efficiency of decodecircuitry. But such regularity or consistency is certainly not requiredfor any of the embodiments of the present invention. For example, wordline segments on different layers may include different numbers ofmemory cells, the memory array may include three memory planes, wordline segments within the first and last array block may be different innumber of memory cells or bit line configuration, and any of many otherirregular variations to the usual consistency of memory array design.Unless otherwise explicitly recited in the claims, such usualregularity, even as shown in the embodiments described herein, shouldnot be imported into the meaning of any claim.

It should be appreciated that the designations top, left, bottom, andright are merely convenient descriptive terms for the four sides of amemory array. The word line segments for a block may be implemented astwo inter-digitated groups of word line segments oriented horizontally,and the bit lines for a block may be implemented as two inter-digitatedgroups of bit lines oriented vertically. Each respective group of wordlines or bit lines may be served by a respective decoder/driver circuitand a respective sense circuit on one of the four sides of the array.

As used herein, a row extends across the entire memory bay (if notacross the entire stripe) and includes many word lines. As used herein abus or line which is “generally spanning the plurality of array blocks”includes spanning almost all the array blocks, such as spanning all butthe last block (e.g., a last block to which a given bus is not coupledto). Such a bus or line may be disposed to the side of the array blocks,or may be disposed above or below such memory array block (i.e., in adirection normal to a semiconductor substrate).

As used herein, “coupling selected bit lines to a first bus” meansrespectively coupling each such selected bit line to a corresponding busline of the first bus. As used herein, word lines (e.g., including wordline segments) and bit lines usually represent orthogonal array lines,and generally follow a common assumption in the art that word lines aredriven and bit lines are sensed, at least during a read operation.Moreover, as used herein, a “global line” (e.g., a global select line)is an array line that spans more than one memory block, but noparticular inference should be drawn suggesting such a global line musttraverse across an entire memory array or substantially across an entireintegrated circuit.

As used herein, a read/write circuit (e.g., a set and read circuit) maybe for one or more data bits, and therefore may be coupled to a singlewire, or may include a separate such read/write circuit coupled to eachbus line of a data bus for each separate bit of data.

As used herein, a “data bus” or data bus “segment” conveysdata-dependent information at least at times, but need not do so at alltimes. For example, such a data bus may convey identical biasinformation on each bus line of such a data bus for certain modes ofoperation. As used herein, a “global” bus may traverse across multiplearray blocks, but need not traverse across (or “span”) the entire memoryarray. For example, such a global bus may traverse across a memory bay,but not necessarily across an entire memory stripe. A “data circuit” mayinclude one or more, or any combination, of a read/write circuit, a setcircuit, a reset circuit, a read circuit, or a program circuit, asappropriate.

As used herein, “selected” lines, such as selected bit lines within anarray block, correspond to such bit lines that are simultaneouslyselected by a multi-headed decoder circuit, and each coupled to acorresponding bus line. Such bit lines may or may not also be selectedby data or I/O circuits to actually perform a given read, program, set,reset, or erase operation. For example, if a 16-headed column decodersimultaneously “selects” and couples 16 bit lines to a given bus (e.g.,SELN bus), it is contemplated that none of the bit lines, one bit line,more than one bit line, or all the bit lines of this group of 16 bitlines, may actually receive a selected bias condition suitable for thegiven mode of operation, while the remaining bit lines may receive anunselected bias condition. Such a bus may be described as being a“data-dependent” bus. In other embodiments, there may be more than onesuch “selected” bias condition conveyed on a given bus, such as when twosimultaneously selected memory cells are to be programmed to differentdata states.

As used herein, a passive element memory array includes a plurality of2-terminal memory cells, each connected between an associated X-line(e.g., word line) and an associated Y-line (e.g., bit line). Such amemory array may be a two-dimensional (planar) array or may be athree-dimensional array having more than one plane of memory cells. Eachsuch memory cell has a non-linear conductivity in which the current in areverse direction (i.e., from cathode to anode) is lower than thecurrent in a forward direction. A passive element memory array may be aone-time programmable (i.e., write once) memory array or a read/write(i.e., write many) memory array. Such passive element memory cells maygenerally be viewed as having a current steering element directingcurrent in a direction and another component which is capable ofchanging its state (e.g., a fuse, an antifuse, a capacitor, a resistiveelement, etc.). The programming state of the memory element can be readby sensing current flow or voltage drop when the memory element isselected.

The directionality of various array lines in the various figures ismerely convenient for ease of description of the two groups of crossinglines in the array. As used herein, an integrated circuit memory arrayis a monolithic integrated circuit structure, rather than more than oneintegrated circuit device packaged together or in close proximity.

The block diagrams herein may be described using the terminology of asingle node connecting the blocks. Nonetheless, it should be appreciatedthat, when required by the context, such a “node” may actually representa pair of nodes for conveying a differential signal, or may representmultiple separate wires (e.g., a bus) for carrying several relatedsignals or for carrying a plurality of signals forming a digital word orother multi-bit signal.

While circuits and physical structures are generally presumed, it iswell recognized that in modern semiconductor design and fabrication,physical structures and circuits may be embodied in computer readabledescriptive form suitable for use in subsequent design, test orfabrication stages as well as in resultant fabricated semiconductorintegrated circuits. Accordingly, claims directed to traditionalcircuits or structures may, consistent with particular language thereof,read upon computer readable encodings and representations of same,whether embodied in media or combined with suitable reader facilities toallow fabrication, test, or design refinement of the correspondingcircuits and/or structures. The invention is contemplated to includecircuits, packaged modules including such circuits, systems utilizingsuch circuits and/or modules and/or other memory devices, relatedmethods of operation, related methods for making such circuits, andcomputer-readable medium encodings of such circuits and methods, all asdescribed herein, and as defined in the appended claims. As used herein,a computer-readable medium includes at least disk, tape, or othermagnetic, optical, semiconductor (e.g., flash memory cards, ROM), orelectronic medium and a network, wireline, wireless or othercommunications medium. An encoding of a circuit may include circuitschematic information, physical layout information, behavioralsimulation information, and/or may include any other encoding from whichthe circuit may be represented or communicated.

The foregoing details description has described only a few of the manypossible implementations of the present invention. For this reason, thisdetailed description is intended by way of illustration, and not by wayof limitations. Variations and modifications of the embodimentsdisclosed herein may be made based on the description set forth herein,without departing from the scope and spirit of the invention. It is onlythe following claims, including all equivalents, that are intended todefine the scope of this invention. Moreover, the embodiments describedabove are specifically contemplated to be used alone as well as invarious combinations. Accordingly, other embodiments, variations, andimprovements not described herein are not necessarily excluded from thescope of the invention.

1. A method for operating an integrated circuit memory array, said memory array comprising a cross-point array of passive element memory cells, each coupled between an associated word line and an associated bit line, said method comprising: in a first mode of operation, biasing selected word lines at a lower voltage than unselected word lines, and biasing selected bit lines at a higher voltage than unselected bit lines; and in a second mode of operation, biasing selected word lines at a higher voltage than unselected word lines, and biasing selected bit lines at a lower voltage than unselected bit lines.
 2. The method of claim 1 wherein: the selected bit line voltage in the first mode of operation is opposite in polarity to the selected bit line voltage in the second mode of operation.
 3. The method of claim 1 wherein: the second mode of operation comprises a block reset operation, during which one or more selected memory cells are reverse biased by biasing one or more selected bit lines at a negative voltage, and by biasing one or more selected word lines at a positive voltage.
 4. The method of claim 3 wherein: the first mode of operation comprises a set operation, during which one or more selected memory cells are forward biased by biasing one or more selected bit lines at a positive voltage, and by biasing one or more selected word lines at a non-negative voltage.
 5. The method of claim 4 wherein: in the first mode of operation, the one or more selected word lines are biased at a ground potential.
 6. The method of claim 3 further comprising biasing, in the second mode of operation, unselected word lines and unselected bit lines at substantially the same voltage, thereby imparting no net bias across unselected memory cells.
 7. The method of claim 6 further comprising biasing, in the second mode of operation, unselected word lines and unselected bit lines at a ground potential.
 8. A method for operating an integrated circuit memory array, said memory array having a plurality of bit lines on a first bit line layer and having a plurality of word lines on a first word line layer, said memory array including a cross-point array of passive element memory cells, each memory cell coupled between an associated word line and an associated bit line, said method comprising: selecting one or more word lines using a word line decoder circuit having a reversible polarity between two modes of operation; wherein the word line decoder circuit sources a current through a selected passive element memory cell in one of the two modes of operation, and sinks a current through the selected passive element memory cell in the other of the two modes of operation.
 9. The method of claim 8 further comprising: selecting one or more bit lines using a bit line decoder circuit having a reversible polarity between two modes of operation.
 10. The method of claim 9 wherein: the bit line decoder circuit comprises a plurality of bit line decoder output nodes, each associated with a respective multi-headed bit line driver circuit; wherein a given multi-headed bit line driver circuit is associated with a data-dependent first source selection bus and a first source bias line.
 11. The method of claim 9 wherein: the memory array comprises a three-dimensional memory array having bit lines on a second bit line layer; and said method further comprises simultaneously selecting a bit line on the first bit line layer and a bit line on the second bit line layer.
 12. The method of claim 11 wherein: each memory cell comprises a reversible resistor element.
 13. The method of claim 12 wherein: said reversible resistor element comprises a transition metal oxide.
 14. The method of claim 12 wherein: each memory cell comprises a reversible resistor element in series with a diode.
 15. The method of claim 10 wherein: each multi-headed bit line driver circuit comprises a respective plurality of bit line driver circuits, each respective bit line driver circuit of a given multi-headed bit line driver circuit responsive to the associated bit line decoder output node, for coupling a respective bit line at times to a respective bus line of the first source selection bus, and for coupling the respective bit line at times to the first source bias line.
 16. The method of claim 15 wherein each bit line driver circuit of a given multi-headed bit line driver circuit respectively consists of: a PMOS device having a source terminal coupled to the respective bus line of the first source selection bus, having a gate terminal coupled to the associated bit line decoder node, and having a drain terminal coupled to the respective bit line, and an NMOS device having a source terminal coupled to the first source bias line, having a gate terminal coupled to the associated bit line decoder node, and having a drain terminal coupled to the respective bit line.
 17. The method of claim 15 wherein: in a first mode of operation, the first source selection bus is data-dependent, with such bus lines established, in accordance with a corresponding data bit for the first mode of operation, at an active or inactive bit line bias condition suitable for the first mode of operation, and the first source bias line is established at the inactive bit line bias condition suitable for the first mode of operation; and in a second mode of operation, the first source bias line is established at an active bit line bias condition suitable for the second mode of operation, and each of the bus lines of the first source selection bus is established at an inactive bit line bias condition suitable for the second mode of operation.
 18. The method of claim 17 wherein: the active and inactive bit line bias conditions suitable for the first mode of operation respectively comprise a first mode selected bit line voltage and a first mode unselected bit line voltage; the active and inactive bit line bias conditions suitable for the second mode of operation respectively comprise a second mode selected bit line voltage and second mode unselected bit line voltage; the first mode selected bit line voltage and the second mode selected bit line voltage are opposite in polarity relative to a ground reference voltage; and the polarity of the bit line decoder is active high in one of the first and second modes, and active low in the other of the first and second modes.
 19. The method of claim 18 wherein: the word line decoder circuit comprises a plurality of word line decoder output nodes, each associated with a respective multi-headed word line driver circuit; wherein a given multi-headed word line driver circuit is associated with a decoded second source selection bus and a second source bias line.
 20. The method of claim 19 wherein: in the first mode of operation, a selected one of the bus lines of the third source selection bus is established, in accordance with corresponding address information, at an active word line bias condition suitable for the first mode of operation, and the other unselected bus lines of the second source selection bus and the second source bias line are established at an inactive word line bias condition suitable for the first mode of operation; and in the second mode of operation, the second source bias line is established at an active word line bias condition suitable for the second mode of operation, and the bus lines of the second source selection bus are established at an inactive word line bias condition suitable for the second mode of operation.
 21. The method of claim 20 wherein each word line driver circuit of a given multi-headed word line driver circuit respectively consists of: a PMOS device having a source terminal coupled to the second source bias line, having a gate terminal coupled to the associated word line decoder node, and having a drain terminal coupled to the respective word line, and an NMOS device having a source terminal coupled to the respective bus line of the second source selection bus, having a gate terminal coupled to the associated word line decoder node, and having a drain terminal coupled to the respective word line.
 22. The method of claim 20 wherein: the active and inactive word line bias conditions suitable for the first mode of operation respectively comprise a first mode selected word line voltage and a first mode unselected word line voltage; the active and inactive word line bias conditions suitable for the second mode of operation respectively comprise a second mode selected word line voltage and second mode unselected word line voltage; the second mode selected word line voltage and the second mode selected bit line voltage are opposite in polarity relative to a ground reference voltage; and the polarity of the word line decoder is active high in one of the first and second modes, and active low in the other of the first and second modes.
 23. The method of claim 20 wherein: the second mode unselected word line voltage and the second mode unselected bit line voltage are substantially the same voltage.
 24. A method for making a memory product, said method comprising: forming a memory array having a plurality of bit lines on a first bit line layer and having a plurality of word lines on a first word line layer, said memory array including a cross-point array of passive element memory cells, each memory cell coupled between an associated word line and an associated bit line; and forming a word line decoder circuit for selecting one or more word lines, said word line decoder circuit having a reversible polarity between two modes of operation; wherein the word line decoder circuit sources a current through a selected passive element memory cell in one of the two modes of operation, and sinks a current through the selected passive element memory cell in the other of the two modes of operation. 